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DEC-I1-HTMAA-D-D

TM11
DECmagtape system

digital equipment corporation · maynard, massachusetts

1st Edition, August 1971
2nd Printing, March 1972
3rd Printing, May 1972
4th Printing, October 1972
5th Printing, February 1973
6th Printing (Rev), June 1973
7th Printing, July 1974
8th Printing (Rev), August 1974

The material in this manual is for infonnationa! purposes and is subject to change
without notice.
Print~d

in U.S.A.

The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
DEC
FLIP CHIP
DIGITAL

UNIBUS

PDP
FOCAL
COMPUTER LAB

CONTENTS
Page
CHAPTER 1 INTRODUCTION
1.1
1.2
1.3
1.3.1
1.3.2
1.3.3
1.4
1.5
1.6

1-1
I-I
1-4
1-4
1-5
1-6

Introduction
Scope
General Description
TUI0 DECmagtape Transport
TM 11 Controller
Magnetic Tape
Specifications
Engineering Drawings
Maintenance

1-6
1-6
1-9

CHAPTER 2 INSTALLATION
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

2-1
2-1
2-1
2-1
2-2
2-2
2-2
2-2

Scope
Configura tion
Unpacking
Inspection
Space Requirements
Power and Cable Requirements
Installation
Final Checkout

CHAPTER 3 OPERATION
3.1
3.2
3.2.1
3.2.2
3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6

Introduction
Controls and Indicators
TUIO DEC magtape Control Panel
TM 11 Controller Maintenance Panel
Operating Procedure
Mounting Tape
Off-Line Operation
On-Line Operation
Restart After Power Failure
Restart After Fail-Safe
Removing Tape

3-1
3-1
3-1
3-6
3-7
3-8
3-9
3-10
3-10
3-11
3-11

CHAPTER 4 PROGRAMMING INFORMATION
4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5

Scope
Device Registers
Status Register (MTS)
Command Register (MTC)
Byte Record Counter (MTBRC)
Current Memory Address Register (MTCMA)
Data Buffer Register (MTD)

iii

4-1
4-1
4-2
4-6
4-8
4-9
4-9

CONTENTS (Cont)
Page
4.2.6
4.3
4.3.1
4.3.2
4.4
4.4.1
4.4.2
4.4.3
4.4.3.1
4.4.3.2
4.4.3.3
4.4.3.4
4.4.3.5
4.4.3.6
4.5

TUIO Read Lines (MTRD)
Interrupts

4-11
4-12

NPR Requests
BR Requests

4-12
4-12

Programming Notes
Rewind Operation
New Drive Selection
Error Handling
Write Operations
Read Operations
Write End of File Operation
Spacing Operations
Write With Extended IRG Operation
Rewind Operation
Program Example

4-12
4-13
4-15
4-15
4-15
4-16
4-17
4-17
4-17
4-17
4-17

CHAPTER 5 THEORY OF OPERATION
5.1
5.2
5.3
5.3.1
5.3.2
5.3.3
5.4
5.5
5.5.1
5.5.2
5.6
5.6.1
5.6.2
5.6.3
5.7
5.8
5.8.1
5.8.2
5.8.2.1
5.8.2.2
5.8.2.3
5.8.2.4
5.8.2.5
5.8.2.6
5.8.2.7
5.8.2.8
5.8.2.9

Introduction
Tape Format
Functional Description
Parity
Gap Shutdown
Function Commands
System Relationship
Address Selection
Address Selector Module
Register Select Logic
Bus Control
NPR Transfers
Interrupt Request
Slave Response
Bus Drivers and Receivers
Registers
Initialize Logic
Command Register (MTC)
Error Bit (15)
Density Bits (14 and 13)
Power Clear Bit (12)
Parity Bit (11)
Unit Select Bits (10, 09, 08)
Control Unit Ready Bit (07)
Interrupt Enable Bit (06)
Extended Bus Address Bits (OS and 04)
Function Bits (03, 02, 01)

5-1
5-2
5-3
5-6
5-7
5-7
5-8
5-8
5-9
5-10
5-12
5-12
5-14
5-15
5-15
5-15
5-16
5-17
5-17
5-18
5-19
5-19
5-20
5-20
5-20
5-21
5-21

CONTENTS (Cont)

5.8.2.10
5.8.3
5.8.3.1
5.8.3.2
5.8.3.3
5.8.3.4
5.8.3.5
5.8.3.6
5.8.3.7

Go Bit (00)
Status Register (MTS)
Illegal Command (15)
End-of-File Bit (14)
Cyclic Redundancy Error Bit (13)
Parity Error Bit (12)
Bus Grant Late Error Bit (11)
End-of-Tape Bit (10)
Record Length Error Bit (09)

5-21
5-22
5-23
5-23
5-23
5-24
5-24
5-24
5-25

5.8.3.8
5.8.3.9
5.8.3.10
5.8.3.11
5.8.3.12
5.8.3.13
5.8.3.14
5.8.3.15
5.8.3.16
5.8.4
5.8.5
5.8.6
5.8.7
5.9
5.9.1
5.9.2
5.9.3
5.9.4
5.10

Bad Tape Error Bit (08)
Non-Existent Memory Bit (07)
Select Remote Bit (06)
Beginning-of-Tape Bit (05)
7-Channel Bit (04)
Settle Down Bit (03)
Write Lock Bit (02)
Rewind Status Bit (01)
Tape Unit Ready Bit (00)
Byte Record Counter (MTBRC)
Current Memory Address Register (MTCMA)
Data Buffer Register (MTD)
TUIO Read Lines (MTRD)
Tape Control
Unit Select
Function Control
Ready and Start Control
Tape Unit Motion Control
Timing Diagrams

5-25
5-26
5-26
5-26
5-26
5-26
5-26
5:"27
5-27
5-27
5-28
5-28
5-29
5-30
5-30
5-30
5-31
5-31
5-32

CHAPTER 6 MODULE DESCRIPTION
6.1
6.2
6.3
6.4

Introduction
DEC Logic
Measurement Definitions
Loading

6-1
6-1
6-1
6-1

APPENDIX A MASTER TAPE TRANSPORT SIGNALS
A.I
A.2

Signals from Master to TMII Controller
Signals from TM 11 Controller to Master

A-I
A-2

ILLUSTRATIONS
Figure No.

Title

Page

1-1

TM 11 DEC magtape System

1-2

3-1

TUI0 Control Panel

3-2

TM II Controller Maintenance Panel
Using TMII Maintenance Panel
Write-Enable Ring
Tape Threading
Tape Loop Limits
Status Register (MTS) Bit Assignments
Command Register (MTC) Bit Assignments
Byte Record Counter (MTBRC) Bit Assignments
Current Memory Address Register (MTCMA) Bit Assignments
Data Buffer Register (MTD) Bit Assignments

3-1
3-6
3-6

3-3
3-4
3-5

3-6
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8

5-1
5-2

5-3

5-4
5-5

5-6
5-7
5-8
5-9

5-10
5-11
5-12

5-13

5-14

Relationship Between Tape Characters and Memory Byte Characters
TUI0 Read Line (MTRD) Bit Assignments
New Drive Selection Flowchart
7-Channel Tape Format
9-Channel Tape Format
EOF Record
TM II System - Simplified Block Diagram
M 105 Address Decoding
Derivatives of GO Signal
Start of Tape Operation
Spacing Forward Three Records
Spacing Reverse Three Records
Spacing Forward Three Records, Bad Tape Error Appearing in First Record

3-9

3-10
3-11

4-2
4-6
4-8
4-9

4-9

4-10
4-11

4-15
5-2

5-3
5-8
5-9

5-10

5-22
5-32
5-32

5-33
5-33

Reading Record of Three Data Characters
Reading Record of Two Tape Characters in Core Dump Mode

5-34
5-35

Writing Record of Three Data Characters
Writing Record of Two Tape Characters in Core Dump Mode

5-36
5-37

TABLES
Table No.
1-1
1-2
1-3
1-4
2-1
3-1
3-2
3-3
4-1
5-1
5-2
5-3
5-4
5-5
5-6
6-1

Title
TM 11 System Manuals
Applicable Documents
TUIO Models
TM II DECmagtape System Specifications
Interconnecting Cables
TUIO DEC magtape Transport Controls
TUI0 DEC magtape Transport Indicators
Maintenance Panel Indicators
Standard Device Register Assignments
Controller Functions
M797 Decoder Selection
Gating and Select Line Signals
Bus Control Functions
Device Register Functions
Core Dump Mode
Module Utilization

vii

Page
1-3
1-3
1-5
1-8
2-2
3-2
3-4
3-7
4-2
5-4
5-11
5-11
5-12
5-16
5-19
6-2

CHAPTER 1
INTRODUCTION

1.1 INTRODUCTION
The TMll DEC magtape System (see Figure 1-1) is a magnetic tape handling system designed to interface with
the PDP-II family of processors and peripherals to provide storage for large amounts of digital information. This
system is ideally suited for writing, reading, and storing large volumes of data and programs in a serial manner:
Transfer of information can be made between the PDP-II and other computer systems, because the TM 11 System
reads and writes in industry-compatible formats.
The basic TM 11 DECmagtape System consists of three distinct components:
TUI0 Tape Transport

A magnetic tape handling device that reads and/or writes information
on magnetic tape in either a 7-channel or 9-channel format. Includes
automatic parity checking and file protection.
Up to eight TU10 transports may be used in one TMII System in
any combination of 7- or 9-channel versions. One transport always
functions as a master for the other system transports.

TM 11 Controller

An interface between the tape units and the PDP-II Unibus. Controls information transfers between the transport and other devices
in a PDP-II System. One controller services up to eight TU 10
transports.
Also referred to as "control unit", "interface", or "magtape control
unit (MTC)".

Magnetic Tape

The recording medium used for data storage. Reel-mounted magnetic tape that is formatted in either 7-channel or 9-channel
industry-compatible format.
Includes end-of-tape (EOT) and beginning-of-tape (BOT) reflective
markers, record gaps, lateral and longitudinal parity characters, and
file marks. In addition, the 9-channel format includes a cyclic
red undancy check character.
Tape is I/2-in. wide with bit packing densities of 200, 556, and
800 bpi for 7-channel; 800 bpi for 9-channel.

1.2 SCOPE
This manual provides the user with the information necessary to operate the TM 11 DECmagtape System and
provides the theory of operation and logic diagrams necessary to understand and maintain the TM 11 Controller.

1-1

Figure 1-1 TM 11 DECmagtape System

This manual and the TUlO DECmagtape Manual (DEC-OO-TVIO-DA) must be used together for a complete
understanding of the entire TM II System. The prime subject matter of this manual is the TM 11 Controller; the
prime subject matter of the TV 10 manual is the tape transport and the magnetic tape. In addition, this manual
serves as an overall system operating guide.
Table 1-1 indicates the coverage in the two manuals, and Table 1-2 lists related PDP-II documents that are
applicable to the TM 11 DECmagtape System.

1-2

Table 1-1
TMII System Manuals
Title

TMll DECmagtape
System Manual

Coverage

Number
DEC-II-HTMA-D

Overall System - description, installation, operation,
programming.
TMII Controller - detailed theory of operation supported by logic diagrams in a second volume.

TU10 DECmagtape
Transport Manual

DEC-oO-TUIO-DA

Tape Transport - description and installation; detailed theory of operation; logic diagrams; maintenance.
Magnetic Tape - detailed description of tape format.

TU10 DECmagtape
Master System
Manual

DEC-oO-TUI0M-D

Master Tape Transport - description, interface and
control, and theory of operation.

Table 1-2
Applicable Documents
Coverage

Number

Title

TU10 DECmagtape

DEC-OO-TU I O-DA

Provides detailed theory, operation, maintenance,
and logic diagrams for the tape transport.

PDP-ll Processor and
Systems Manuals

A series of maintenance and theory manuals that
provide a detailed description of the basic PDP-II
System.

PDP-ll Processor
Handbook

A general handbook that discusses system architecture, addressing modes, the instruction set, programming techniques, and software.

PDP-ll Peripherals
Handbook

112-00973-2908

A handbook devoted to a discussion of the various
peripherals used with PDP-II systems. It also provides
detailed theory, flow, and logic descriptions of the
Unibus and external device logic; methods of interface
construction; and examples of typical interfaces.

*Applicable manuals are furnished with the system at time of installation. The document number depends upon the specific
PDP-II family processor.
**Use the processor handbook unique to the actual CPU.

1-3

Table 1-2 (Cont)
Applicable Documents
Title

Number

Coverage

Logic Handbook

DEC, 1971

Presents functions and specifications of the M-Series
logic modules, accessories, and connectors used in
the TM 11 Controller and the TU 10 Tape Transport.
Includes other types of logic produced by DEC but
not used with PDP-II devices.

Paper-Tape Software
Programming Handbook

DEC-II-GGPB-D

Provides a detailed discussion of the PDP-II software
system used to load, dump, edit, assemble, and debug
PDP-II programs; input/output programming; and
the floating-point and math package.

1.3 GENERAL DESCRIPTION
The TM 11 DECmagtape System is a magnetic tape storage facility consisting of a TM 11 Controller and up to eight
TUIO DEC magtape transports. The system reads or records digital data, in parallel, on magnetic tape in either a
7- or 9-channel industry-compatible format. Transfer rates as high as 36,000 characters per second can be achieved.
One tape transport is referred to as the master and contains all of the magnetic tape electronics. Additional transports are referred to as slaves and share the electronics in the master. This is possible because only one transport
can communicate with the processor at any given time. Any combination of 7- and 9-channel transports (up to a
total of eight) may be used with one TM 11 Controller.
The TM 11 DECmagtape System has a number of features that improve its reliability and make it exceptionally
useful as a storage device. A read-after-write head automatically checks parity character-by-character; a longitUdinal parity check (LPC) is automatically performed on all units; and a cyclic redundancy check (CRC) is automatically performed on 9-channel units.
Compatibility with industry standards provides efficient transfer of data between the PDP-II and other computer
systems. The tape format for both 7- and 9-channel transports is compatible with all industry standards.
The three major functional components of a TM II DECmagtape System are: the TUI 0 DECmagtape Transport,
the TMll Controller, and the magnetic tape. Each of these functional components is briefly described in subsequent paragraphs.
1.3.1 TUI0 DECmagtape Transport
The TUI0 DECmagtape Transport is a solid-state, magnetic tape handling device that controls tape motion and
reads or records digital information on magnetic tape in industry-compatible formats.

The TU lOuses vacuum columns and a servo-controlled single capstan to control tape motion. The only contact
with the oxide surface is the magnetic head and a rolling contact on one low-friction, low-inertja bearing. Dancer
arms and pinch rollers, which shorten tape life and can cause errors, are not used in the TUlO.
Tape transport commands can be issued manually from the TUI 0 control panel or remotely from the processor
by means of the TMII Controller. Indicators on both the transport and the controller indicate transport status.
Each tape transport (master or slave) consists of the TV 10 cabinet, reel and reel motor control, capstan drive, and
read/write components. In addition to these components, the master transport contains logic circuits that: start
and stop any tape unit, generate the read and write pulses, generate the required gaps, generate parity, and check
parity. These logic circuits are shared by all transports under control of the master and the TM II Controller.
In addition to the parity checking features of the TUIO, the transport contains deskewing electronics to eliminate
static skew, and write-protect ring sensing.
There are 16 different TUI0 models. The different models are listed in Table 1-3.
Table 1-3
TUlOModels
No. 0 f Channels

Type of Unit

60Hz

115 Vac
50Hz

60Hz

230 Vac
50Hz

9-channel

Master
Slave

TUIO-EA
TUIO-EE

TUIO-EC
TUIO-EH

TUIO-EB
TUIO-EF

TUIO-ED
TUIO-EJ

7-channel

Master
Slave

TUIO-FA
TUIO-FE

TUIO-FC
TUIO-FH

TUIO-FB
TUI0-FF

TUIO-FD
TUIO-FJ

NOTES:

1. TMll-A Controller used with all 115 Vac models (50/60 Hz)
TM II-B Controller used with all 230 Vac models (50/60 Hz)

2. Model codes are used as follows:
channel designation

power designation

Channel designation:

E = 9-channel unit
F = 7-channel unit

Power designation:

Master = A-lIS Vac)
B - 230 Vac

60 Hz

C - 115 Vac)
D - 230 Vac

50 Hz

Slave

E - 115
F - 230
H - 115
J - 230

Vac)
Vac
Vac)
Vac

60 Hz
50 Hz

1.3.2 TMII Controller
The TM 11 Controller is the interface between the tape transport and the Unibus. Thus, it controls command and
data transfers between the tape trans'port and any device connected to the bus, such as the processor or memory.
One controller can handle up to eight TU 10 DECmagtape Transports.
Basically, the controller consists of six major registers that have been assigned standard bus addresses and can be
loaded or read by any PDP-II instruction referring to that address. Four of the registers can be loaded or read
from the bus, the remaining two registers can only be read from the bus.
1-5

The controller has three main functions: handling data transfers, issuing control commands, and monitoring
operation of the system.
During data transfer functions, the controller assembles the data word from the magnetic tape and places it on the
bus (read operation), or assembles it from the bus and loads it into the tape transport read/write heads (write
operation) for recording on magnetic tape. The commands necessary to perform the specified operation are generated by the controller under program control.
Nonnal data word transfers are perfonned by direct memory access transactions at the NPR level. If the controller is ready to begin a new function or if an error condition exists, it issues an interrupt request so that it can be
serviced by the program.
In addition to the commands required for data transfers, the controller may issue other commands governing
tape unit selection, direction of tape travel, rewind, space forward, space reverse, write end-of-file mark, etc. The
controller also monitors various functions and provides an indication of error conditions. The status of the
monitored functions is stored in one of the controller registers.
A controller maintenance panel permits clearing of the TM 11 System and includes 28 indicator lights to represent
error conditions and the status of selected functions.
1.3.3 Magnetic Tape
The magnetic tape is the recording medium used with the TM II DECmagtape System. The tape is 1/2-in. oxideThe tape includes reflective end-of-tape (EOT) and beginning-of-tape (BOT) markers and is
coated Mylar
stored on 2400-ft reels.

8 .

Data is recorded in an industry-standard format. The 7-channel format consists of six data channels (I, 2, 4, 8, A,
and B) and a parity channel (C). Each PDP-II word is divided into two 6-bit characters. Data is stored in variablelength records separated by interrecord gaps of 3/4 in. A longitudinally parity check (LPC) character is written at
the end of each record. Standard fonnat marks (tape mark, group mark, segment mark, etc.) may also be written
in a record along with the data. The 7-channel fonnat may be written in densities of 200,556, or 800 bpi.
The 9-channel format consists of eight data channels in the following order: 9,8,7,6,5,4,3, 2, and 1. Channel
4 is used for parity. In addition, a cyclic redundancy check (CRC) character is written before the LPC character.
Data is stored in variable length records separated by interrecord gaps of one-half inch. Each PDP-II word consists of two 8-bit characters. The 9-channel format always has a bit packing density of 800 bpi.
Both formats are written by means of the non-return-to-zero (NRZI) recording method. Although the tape has
two basic states of magnetization, the state does not determine the value of the bit. A logical 1 is represented by
a change of magnetization in either direction. A logical 0 is represented by a constant state of magnetization.

1.4 SPECIFICATIONS
Operating and physical specifications for the TMII Controller, the TUIO DECmagtape Transport, and the magnetic tape are given in Table 1-4.
1.5 ENGINEERING DRAWINGS
A complete set of reduced engineering drawings and module circuit schematics are provided in a companion

volume to this manual, which is entitled, TM11 DECmagtape System, Engineering Drawings. A list of individual
modules is included in Chapter 6 of this manual. The general logic symbols used on these drawings are described
in the DEC Logic Handbook, 1971.

Mylar is a trademark of DuPont Corporation.

1-6

Table 1-4
TMtlDECmagtape System Specifications
Tape Characteristics
Capacity:

2400 ft of I/2-in., industry standard, I-mil Mylar tape.

Reel Diameter:

10-1/2 in. standard reels

Tape Handling:

Direct-drive reel motors; servo-controlled single capstan;
vacuum tape buffer chambers with constant tape winding
tension.

Tape Speed:

45 in. per second, reading and writing

Rewind Speed:

150 in. per second (approximately 3-minute rewind time
for 2400-ft reel)

Packing Density:

7-channel - 200, 556, and 800 bpi, selectable under program control
9-channel - 800 bpi

Data Recording and Transfer
Recording Mode:

NRZI, industry-compatible

Magnetic Head:

Dual gap, read-after-write

Data Transfers:

Direct memory access (non-processor request)

Transfer Rate:

36,000 characters per second, maximum

BOT, EaT Detection:

Photoelectric sensing of reflective strip, industrycompatible.

Write Protection:

Write-protect ring sensing

Data Checking:

Read-after-write parity checking; longitudinal redundancy
check; cyclic redundancy check (9-channel only).

Interrecord Gap:

Reads tape with gap of 0.48 in. or more; writes tape with
gap of 0.52 in. or more (compatible with industry standard).

Programmable Commands Accepted by TUt 0
Rewind and go off-line
Read
Write
Write end-of-file (EOF) character
Space forward
Space reverse
Write with extended interrecord gap (IRG)
Rewind to beginning of tape (BOT)
Controller Register Addresses
Status Register (MTS):

772520

Command Register (MTC):

772522

Byte Record Counter (MTBRC):

772524

1-7

(read only)

Table 1-4 (Cont)
TM 11 DECmagtape System Specifications
Controller Register Addresses (Cont)
Current Memory Address Register
(MTCMA):

772526

Data Buffer Register (MTD) :

772530

TUIO Read Lines (MTRD):

772532

(read only)

Interrupt
Priority Level:

BR5

Vector Address:

224

Local Transport Controls
PWR ON/PWR OFF

power control switch

ON-LINE/OFF-LINE

local or programmed operation

START/STOP

tape motion control

LOAD/BR REL

releases tape for loading

UNIT SELECT

selects unit for program control

FWD/REW /REV

tape direction control

TUI0 DECmagtape Transport
Mounting:

Mounts in standard H960C-A cabinet.

Size:

26 in. high, 19 in. wide, 25 in. deep

Cooling:

Internally-mounted fans

Controls:

Front panel mounted

TM 11 Controller
Mounting:

Mounts in standard 19-in. rack; normally mounted in
cabinet containing master tape transport.

Size:

10-1/2 in. high, 19 in. wide

Controls:

On separate maintenance panel card that plugs into controller; includes CLEAR switch and 28 indicators displaying status of selected system functions.

Environmental Conditions
Temperature:

40°F to 110°F for system
60°F to 80°F for magnetic tape

Humidity:

20% to 95% (non-condensation) for system
40% to 60% (non-condensation) for tape

1-8

Table 1-4 (Cont)
TM11 DECmagtape System Specifications
Power Input Requirements
Controller:

either lIS Vac, 50/60 Hz at 6.25A (A model)
230 Vac, 50/60 Hz at 6.25A (B model)
or

TU I O-EA, EE, FA, FE

lIS Vac, 60 Hz

TU 1O-Ee, EH, FC, FH

115 Vac, 50 Hz

TUIO-EB, EF, FB, FF

230 Vac, 60 Hz

TUIO-ED, EJ, FD, FJ

230 Vac, 50 Hz

Power and Cabling
TMII Power:

System power supplied by one H720 Power Supply
mounted at back of master cabinet. Provides +5V at
16A and -15V at lOA for use by TMl1 and up to eight
TUI0s.

TUIO Power:

Tape transport power (reel motors and fans) provided by
internal power supply in each transport.

Cabling:

BC ll-A cable to connect controller to Unibus and to connect command signals between controller and master TUI O.
M908 ribbon connector to connect master TU 10 to slave
TUIOs.

1.6 MAINTENANCE
The basic maintenance philosophy of the TM II DECmagtape System is to present the user with the information
necessary to understand normal operation of the system. The user can utilize this information when analyzing
trouble symptoms to determine necessary corrective action. It is beyond 'the scope of this manual to present detailed troubleshooting information.
Detailed maintenance and troubleshooting information of the TUIO DECmagtape Transport is given in the TUIO
DECmagtape Manual, DEC-OO-TUIO-DA.

1-9

CHAPTER 2
INSTALLATION

2.1 SCOPE
This chapter covers general infonnation on installation of the TM 11 DECmagtape System. Detailed information
on installation of the TVI 0 Tape Transport is presented in the TV] 0 DECmagtape Transport Manual,
DEC-OO-TVIO-DA. Infonnation on various mounting cabinets is presented in the H720 Power Supply and

Mounting Box Manual, DEC-II-HRSB-D.

2.2 CONFIGURATION
Installation procedilres vary greatly, depending on the system configuration. For example, if the user has ordered
a complete PDP-II System, the TMII DECmagtape System is shipped already installed in its appropriate rack
together with the required cables. If the complete system is shipped, the interconnecting cables are already installed.
However, if only a part of the system is shipped because the user already has a basic PDP-II System, then the

TM 11 DECmagtape System is shipped separately together with the appropriate cables. Installation procedures
may vary, depending on whether the unit is mounted in a DEC- or customer-supplied cabinet, the number of tape
transports in the system, and other variable factors.

2.3 UNPACKING
The equipment should be unpacked as follows:
Procedure

Step

Place the equipment package within the installation site near its final location.
Cut the shipping straps and carefully remove all packing material.

Remove the machine screws that hold the cabinet to the shipping pallet. Slide
the cabinet off the pallet and move it to its final location.

Remove any tape holding the modules in place within the mounting panels and
any tape holding the power and interconnecting cables to the floor of the
cabinet.

2.4 INSPECTION
Inspect all of the equipment before installing it, checking each piece against the parts list. Any damage must be
reported immediately to the shipper and to the DEC representative.

2-1

2.5 SPACEREQUIREMENfS
No special site preparation is required for installation of the TM 11 DECmagtape System. However, when installing
the system, make certain that the front and rear of the cabinets are accessible to maintenance personnel. If the
cabinets are separated by long distances, consideration should be given to overhead trenching ducts or floor ducts
for the cabling.
2.6 POWER AND CABLE REQUIREMENTS
The TM 11 Controller and associated TUI0 transports operate from a line voltage of either 115 Vac or 230 Vac
at a frequency of either 50 or 60 Hz, depending on the model ordered by the customer. The maximum current
required is 6.25A for the controller. The TMII Controller contains its own power supply, and each TUI0 transport has its own power supply. Power supply specifications are listed in Table 1-4. The interconnecting cables
are listed in Table 2-1.
Table 2-1
Interconnecting Cables
Function

Cable
BC II-A Cable

Connects TMII Controller to PDP-II Unibus and to TUIO
master transport.

M908 Ribbon Connector*

Connects command and analog signals between master transport and slave transports.

*Number of cables supplied dependent on number of transports in system.

2.7 INSTALLATION
If the TM II DECmagtape System is shipped separately, there are only three components that must be installed:
the TMl1 Controller, the TUIO DECmagtape Transport (or transports), and the H720 Power Supply. The TMll
Controller is 19 in. wide and 10-1/2 in. high; therefore, it can be mounted in any standard 19-in. rack or cabinet.
Installation of the power supply and tape transport are covered in the appropriate manuals referenced in Paragraph 2.1.
2.8 FINAL CHECKOUT
After the system is installed and all cables connected, a final checkout should be performed. The fIrst step is to
apply power and check all manual controls of the transports, power clear operation, etc. The second step is to run
the diagnostics supplied with the system.

2-2

CHAPTER 3
OPERATION

3.1 INTRODUCTION
This chapter provides the information necessary to operate the TM 11 DECmagtape System. The description is
divided into two major parts: controls and indicators, and operating procedures.
The description of the controls and indicators (refer to Paragraph 3.2) is in tabular form and provides the user
with the type and function of each operating switch and indicator on the TVI 0 DECmagtape Transport and the
TM 11 Controller maintenance panel.
Step-by-step operating procedures for both on-line and off-line system operation are given in Paragraph 3.3.
Complete maintenance-type procedures and adjustments for the TVIO are beyond the scope of this manual and
are covered in the TV 10 DECmagtape Manual.
3.2 CONTROLS AND INDICATORS
The controls and indicators used to operate the TM 11 DECmagtape System are detailed in the following paragraphs. These paragraphs describe the TV 10 DECmagtape Transport control panel and the TM 11 Controller
maintenance panel.

liLDll

3.2.1 TVIO DECmagtape Control Panel

I PWR IILOADII ROY ~ END
LEI
PT WI
PROT

The TM 11 DECmagtape System is controlled by switches mounted
on the control panel of the TV 10 transport. These switches can be
used for off-line (manual or local) operation of the transport or can
be used to enable the TM 11 Controller for on-line (or remote) operation under program con trol.
The TV 10 tape transport control panel (see Figure 3-1) is the small
control panel located at the lower left of the TV 10 front panel.
Table 3-1 lists all tape transport controls and includes the type and
function of each. Table 3-2 lists the tape transport indicators.

I~I~EIEJIWRTII FWDIIREV IIREWI
PWR ON

ON· LINE

START

PWR OFF

OFF'LINE

STOP

The controls shown in Figure 3-1 are those used during normal system operation. Additional controls, such as the adjustments to vary
tape speed, control capstan acceleration and deceleration times, and
reduce mechanical and electrical skew, are tape transport mainten-

FWD

LOAD

BR REL

UNIT
SELECT

REW

REV

CP-0093

ance adjustments and are beyond the scope of this manual.
Figure 3-1 TVIO Control Panel

3-1

Table 3-1
TU 10 DECmagtape Transport Controls
Control
PWR ONjPWR OFF
switch

Type
2-position
butterfly switch

Function
Applies primary power to the TUIO tape transport.
Primary power must be turned on at each individual tape transport; not remotely controlled from the system.
PWR ON position - applies ac power to primary power supply
transformer T 1 and illuminates PWR indicator light.
PWR OFF position - deactivates ac power, thereby removing all
power from the transport.

ON-LINE/
OFF-LINE switch

2-position
butterfly switch

Controls local (off-line) and remote (on-line) operation of the
tape transport.
ON-LINE position - allows on-line system operation under program control.
Read/write heads are not connected to the TM II Controller
until the program selects the tape transport.
Tape transport is not completely on-line until the transport has
been selected by the program (SEL bits in command register).
Unit is completely on-line when SEL and RDY indicators are lit.
OFF -LINE position - disconnects the transport from the TM 11
Controller to allow manual off-line operation.
Tape motion is controlled by the FWD/REW/REV and START/
STOP switches when in off-line mode.
Tape unit cannot be remotely selected when switch is in OFFLINE position.

START/STOP
switch

2-position
butterfly switch

Controls starting and stopping of tape.
START position - if transport is off-line, initiates tape motion
in the direction determined by setting of the FWD/REWfREY
switch.
This position has no effect on tape motion if transport is in online (remote) mode.
STOP position - stops all tape motion in off-line mode except
rewind.
Does not stop transport during rewind mode of operation.

3-2

Table 3-1 (Cont)
TUIO DECmagtape Transport Controls
Control
LOAD/BR REL
switch

Type
3-position
butterfly switch

Function
LOAD position - energizes the vacuum system to place the
transport in a ready status to accept either on-line or off-line
commands. Tape is drawn into the buffer columns fonning
a tape loop between the vacuum switches.
Switch must always be in LOAD position when operating the
transport either locally (off-line) or remotely (on-line).
Lights LOAD indicator.
BR REL position - deenergizes the vacuum system and removes
the tape reel motor braking action. The tape reels can be manually rotated, because there is no vacuum tension on the tape.
Used primarily for loading and removing tape from transport.
Center position - the vacuum system is deenergized and the
brakes are locked.

UNIT SELECT
switch

8-position
thumbwheel
switch
Each position has
corresponding indicator number.
These are numbers 0 through 7.

Pennits remote selection of a tape transport by the program.
The tape transport is selected for use when the TM 11 Controller's selection code (SEL bits in the command register) corresponds to the numeral on the UNIT SELECT switch.
When a tape transport is selected by the con troller and the
ON-LINE/OFF-LINE switch is set to ON-LINE, the ON-LINE
and SEL indicators light to indicate that the tape unit is fully
on-line.
When using more than one tape transport, make certain that
each transport is dialed to a different number.

FWDjREW /REV
switch

3-position
butterfly switch

Moves tape in selected direction, depending on activation of the
START/STOP switch. Used during off-line (local) operation of
the transport.
If the tape is moving in one direction, moving this switch to a

different setting has no effect unless the tape is first stopped by
START/STOP switch. The required sequence is given in
Paragraph 3.3.2.
FWD position - tape is moved in the forward direction until the
EOT (end-of-tape) marker is sensed, at which time tape motion
stops.
Causes FWD indicator to light.

3-3

Table 3-1 (Cont)
TUI0 DECmagtape Transport Controls
Control

Type

Function
REW position - tape is moved in the reverse direction, rewinding it onto the feed reel until the BOT (beginning-of-tape) marker is sensed, at which time tape motion stops.

FWD/REW /REV
switch (cont)

After the BOT marker has been reached, depressing the switch
again causes the tape to continue to rewind until it is completely
rewound onto the feed reel or until the switch is deactivated.
Causes REW indicator to light. During this mode, tape moves
at a much faster speed than during the REV mode.
Tape rewinds to a point well beyond the BOT marker, then
stops, moves forward until the BOT marker is again sensed,
then comes to a complete stop.
REV position - tape is moved in the reverse direction until the
BOT marker is sensed, at which time tape motion stops.
Causes REV indicator to light.

Table 3-2
TUI0 DECmagtape Transport Indicators
Indicator
PWR indicator

Type
single light

Function
When lit, indicates that primary power has been applied to the
TUIO transport.
Controlled by PWR ON/pWR OFF switch.

LOAD indicator

single light

When lit, indicates that the vacuum system has been enabled,
tape has been drawn into the buffer columns forming the required tape loop, and the transport is ready to accept either online or off-line commands.
Controlled by LOAD/BR REL switch.

RDY indicator

single light

When lit, indicates that all read/write circuits and input/output
lines are enabled; thus, the transport can accept processor commands provided the SEL indicator is also lit.

LD PT (load point)
indicator

single light

When lit, indicates that the beginning-of-tape (BOT) marker has
been sensed, and the transport is ready for operation.
Tape motion stops when the BOT marker has been sensed.
When LD PT is lit, the transport does not accept a rewind
(REW) command but does accept forward (FWD) and reverse
(REV) commands.

Table 3-2 (Cont)
TUIO DECmagtape Transport Indicators
Indicator
END PT (end point)
indicator

Function

Type
single light

When lit, indicates that the end-of-tape (EOT) marker has been
sensed. When this marker is sensed, all tape motion stops to
prevent tape from winding off the reel.
When the END PT indicator is lit, the transport does not accept
a forward (FWD) command but does accept a reverse (REV) or
rewind (REW) command.

FILE PROT
(file protect)
indicator

single light

When lit, indicates that writing on the magnetic tape is inhibited.
This indicator lights if no file reel is mounted on the feed reel
hub or if a file reel is mounted that does not have a write-enable
ring installed.
When the FILE PROT indicator lights, the master tape unit
sends a WRL (write lock) signal to the TM 11 Controller. This
signal sets the WRL bit in the status register and prevents the
controller from performing a write operation.

OFF-LINE
indicator

single light

When lit, indicates that the transport can be operated manually
by using the switches on the transport control panel.
Transport cannot be operated under program control when this
ligh t is Ii t.

SEL (select)
indicator

single ligh t

When lit, indicates that the transport has been properly selected
by the controller and is completely on-line. The transport can
now receive data from the controller and write it on the magnetic tape, or read data from the tape and transmit it to the controller for storage in memory.
The SEL indicator lights when the number represented by the
SEL bits in the command register corresponds to the number
dialed on the transport UNIT SELECT switch.

WRT (write)
indicator

single light

When lit, indicates that the write-enable ring has been installed
on the feed reel, and the transport can write on the magnetic
tape.

FWD (forward)
indicator

single light

When lit, indicates tape is moving in the forward direction.

REV (reverse)
indicator

single light

REW (rewind)
indicator

single light

Controlled by FWD position of FWD/REW/REV switch.
When lit, indicates that tape is moving in the reverse direction.
Controlled by REV position of FWD/REW /REV switch.
When lit, indicates that tape is being rewound. Tape continues
rewinding until BOT marker is sensed or until START/STOP
switch is set to STOP.
Controlled by REW position of FWD/REW /REV switch.

3-5

3.2.2 TMll Controller Maintenance Panel

The TM 11 Controller maintenance panel is a small plug-in card containing switches and indicators that are used
primarily for monitoring system functions during maintenance operations. Figure 3-2 illustrates the panel itself,
and Figure 3-3 indicates how the panel is plugged into the system when it is to be used.

SOWN

WRL

RWS

TUR

FCTN
BIT2

FCTN
BITI

FCTN
BITO

NXM

SELR

BOT

7CH

PEVN

CU
ROY

INT
ENB

BGL

EOT

RLE

BTE

UNIT
SEL2

UNIT
SEll

UNIT
SELO

ILC

EOF

CRE

PAE

ERR

DEN8

DEN5

CLEAR

a. Maintenance Panel Indicators
STATUS REGISTER
(MTS) BITS

COMMAND REGI STER
(MTC) BITS*

CLEAR

* When

an indicator is lit. it indicates that the associated
register bit is set.
11-0390

b. Bits Monitored by Indicators

Figure 3-2 TM 11 Controller Maintenance Panel

MASTER
TAPE UNIT

I"'"

PLUG

,II'J

TMll CONTROLLER
MAINTENANCE PANEL

TMI1 CONTROLLER
MODULE RACK

\1-0393

Figure 3-3 Using TM 11 Maintenance Panel

3-6

Although there are four toggle switches on the panel, only the CLEAR switch is used in the TM 11 System. When
actuated, this switch clears the TM II Controller, the master tape transport, and all slave tape transports. It does
not, however, clear any other system components such as the processor.
The 28 indicator lights on the panel monitor bits from the controller status register (MTS) and command register
(MTC). The bits that are monitored are shown in Figure 3-2b and listed in Table 3-3. A brief description of each
indicator function is presented in Chapter 4, which describes each bit position of all controller registers. A more
detailed description is presented in Chapter 5.
Table 3-3
Maintenance Panel Indicators
Indicator
SDWN
NXM
BGL
ILC
WRL
SELR
EDT
EOF
RWS
BOT
RLE
PAE
TUR
7CH
BTE
CRE
FCTN BIT2
PEVN
UNIT SEL2
ERR
FCTN BITl
CURDY
UNIT SELl
DEN 8
FCTN BITO
INT ENB
UNIT SELO
DEN 5

Name
Settle Down
Non-Existent Memory
Bus Grant Late
Illegal Command
Write Lock
Select Remote
End-of-Tape
End-of-File
Rewind Status
Beginning-of-Tape
Record Length Error
Parity Error
Tape Unit Ready
7 Channel
Bad Tape Error
Cyclical Redundancy Error
Function Bit 2
Parity Even
Unit Select Bit 2
Error
Function Bit 1
Control Unit (controller) Ready
Unit Select Bit 1
Density 8 Bit
Function Bit 0
Interrupt Enable
Unit Select Bit 0
Density 5 Bit

Bit

MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTS
MTC
MTC
MTC
MTC
MTC
MTC
MTC
MTC
MTC
MTC
MTC
MTC

03
07
11
15
02
06
10
14
01
05
09
12
00
04
08
13
03
II
10
15
02
07
09
14
01
06
08
13

3.3 OPERATING PROCEDURE
The TMII DEC magtape System can be used in either an on-line or off-line operating mode. The off-line mode
(also referred to as local or manual mode) is controlled by switches on the front panel of the master tape unit
cabinet and the controls on the individual slave tape units. The on-line mode (also referred to as remote or
program-controlled mode) is controlled by programmed commands from the PDP-II System.

3-7

The following paragraphs present procedures for operating the TM 11 DECmagtape System. Both on-line and offline procedures are discussed. Although procedures are included for setting up on-line operation, it is beyond the
scope of this chapter to present any detailed programming information. Programming infonnation, along with
references to other programming aids, is included in Chapter 4.
Whenever handling magnetic tapes and reels, it is important to observe certain precautions to prevent loss of data
and/or damage to tape handling equipment. These precautions are:
a.

Always handle a tape reel by the hub hole; squeezing the reel flanges can cause damage to the
tape edges when winding or unwinding tape.

Never touch the portion of tape between the BOT and EOT markers. Oils from fingers attract
dust and dirt. Do not allow the end of the tape to drag on the floor.

Never use a contaminated reel of tape; this spreads dirt to clean tape reels and can affect tape
transport operation.

Always store tape reels inside their containers. Keep empty containers closed so dust and dirt
cannot get inside.

Inspect tapes, reels, and containers for dust and dirt. Replace take-up reels that are old or
damaged.

Do not smoke near the transport or tape storage area. Tobacco smoke and ash are especially
damaging to tape.

Do not place the DECmagtape transport near a line printer or other device that produces paper
dust.

Clean the tape path frequently.

3.3.1 Mounting Tape
Before using the TMII DECmagtape System in either mode, it is necessary to make certain that magnetic tape is
properly loaded and threaded in the TUIO Tape Transport. The following procedure is used for mounting tape:
Step

Procedure
Apply power to the transport by depressing the PWR ON switch.

Ensure that the LOAD/BR REL switch is in the center position (this applies the
brakes).

Place a write-enable ring (see Figure 3-4) in the groove on the file reel if data is
to be written on the tape.
If writing or erasing is not required, make certain there is no ring in the groove.

Mount the file reel onto the lower hub with the groove facing towards the back.
Ensure that the reel is firmly seated against the flange of the hub.

Install the take-up (top) reel in the same manner as described in Step 4 above.

Place LOAD/BR REL switch to the BR REL position.

Unwind tape from the file reel and thread the tape over the tape guides and head
assembly as shown in Figure 3-5.

Wind about five turns of tape onto the take-up reel.

3-8

Procedure

Step

9
10

Set the LOAD/BR REL switch to the LOAD position to draw tape into the
vacuum columns.
Select FWD and depress the START switch to advance the tape to the load point.
When the BOT marker is sensed, tape motion stops, the FWD indicator goes out,
and the LOAD PT indicator comes on.
NOTE
If tape motion continues for more than 10 seconds,
depress STOP, select REV (reverse), and then depress
START. The tape should advance to the BOT marker
(load point) before stopping.

Figure 3-4 Write-Enable Ring
3.3.2 Oft-Line Operation
Off-line operation of the TU I 0 Tape Transport is used primarily for loading and unloading magnetic tape, for
positioning magnetic tape prior to on-line operation, and for controlling tape motion during maintenance. During
off-line operation, tape motion is controlled by the switches on the TUIO control panel.
Althouah there are no specific operating procedures for off-line operation (other than that the ON-LINE/OFFUNE switch must be in OFF-LINE), the following switch restrictions should be noted:

3-9

TAPE

GUIDE~.~_..============7'

TRANSPORT WILL
AUTOMATICALLY
(FAIL-

TAPE

SAF~H~JNg~r6~)

POSITIVE
TAPE TENSION
...----HOLDS TAPE AGAINST
CAPSTAN

TR\I'
___ /
I II' -'8
1

WIL~;i:Hil~~~~O~~)+

RIW ERASE HEAD ASSEMBLY

[I"I " \__ .',-'

NOTE'TAPE IS AUTOMATICALLY

INTO VACUUM COLUMNS
--.J~ DRAWN
WHEN LOADI BR REL SWITCH
H(--'~S
T:~:
:~,~:AD
POSITION
/

TAPE WILL BE EXTRACTED
:
FROM C O L U M N T h '
(TAKE'UP REEL TURNED ON)
TRANSPORT WILL

AUT~~~i'bAcf~~

(FAIL-SAFE CONDITION)

/'::1

"-8-'

LEFT VACUUM COLUMN

' , __

I\
I '\\",;
: ,

- - -

,/,
:

L?
7-

VACUUM CHAMBER PORT

(TO VACUUM MOTOR)

FILE REEL

TURNED ON

II,.

'II

1 "

RIGHT VACUUM

I K\COLUMN

i,.':

~'-J':
II:
\-8-'

Ii \~ ":I'",

I~'

Figure 3-5 Tape Threading

When the tape is traveling in any direction, resetting the FWD/REW/REV switch to any other
position has no effect on tape travel. The START/STOP switch must first be set to STOP, the
FWD/REW/REV switch reset, and then the START/STOP switch set to START.

When the tape load point (BOT marker) is reached, the transport does not accept a rewind
(REW) command.

When the tape end point (EOT marker) is reached, the transport does not accept a forward
(FWD) command.

3.3.3 On-Line Operation
On-line operation of the TUIO Tape Transport is used when the tape transport is under program control. Setting
the ON-LINE/OFF-LINE switch to ON-LINE allows the transport to accept commands from the controller when
the transport is selected by the program. Thus, the transport is not fully on-line until the transport RDY and SEL
indicators are lit.

3.3.4 Restart After Power Failure
In the event of a power failure, the DECmagtape transport automatically shuts down, and tape motion stops without damage to the tape. Return of power is indicated when the PWR indicator lights. At this time, the transport
can be restarted as follows:

3-10

Step

Procedure
Set LOAD/BR REL switch to BR REL position to release the brakes.

Manually wind the reels to take up any tape slack.

Set the LOAD/BR REL switch to LOAD position to draw tape into the vacuum
columns.

Set ON-LINE/OFF-LINE switch to desired position and resume desired operation.

3.3.5 Restart After Fail-Safe
If the tape loop in either buffer column exceeds the limits shown in Figure 3-6, the vacuum system automatically
shuts down, and tape motion stops without damage to the tape. When this fail-safe condition occurs, the tape
transport does not respond to either on-line or off-line commands. To restart the transport after fail-safe, perform
the same procedures as for restarting after power failure (refer to Paragraph 3.3.4).

VACUUM
SWITCHES
NORMAL
OPERATING
LIMITS

10
I
I

SHORT LOOP
(TRANSPORT
WILL SHUTDOWN)

~./
, , _ ....

BUFFER
COLUMN

NORMAL
OPERATING
LIMITS
LONG LOOP

~io"'"---(TRANSPORT

WILL SHUTDOWN

CP-0088

Figure 3-6 Tape Loop Limits
3.3.6 Removing Tape
The following procedure describes the method for removing tape from the TUIO Tape Transport.
Step

Procedure
Make certain that ON-LINE/OFF-LINE switch is set to the OFF-LINE position.

Set START/STOP switch to STOP position.

Set FWD/REW /REV switch to REW position.

Set START/STOP switch to START position. The tape should rewind until the
BOT marker is reached.

3-11

Procedure

Step
5

Set LOAD/BR REL switch to BR REL position to release the brakes.

Gently hand wind the file reel in a counterclockwise direction until all of the
tape is wound onto the reel.
CAUTION
When hand winding the tape, do not jerk the reel. This may
stretch or compress the tape, which can cause irreparable
damage.

Remove the me reel from the hub assembly.

3-12

CHAPTER 4
PROGRAMMING INFORMATION

4.1 SCOPE
This chapter presents general programming information for software control of the TM 11 DECmagtape System.
Although a typical program example is included in this chapter, it is beyond the scope of this manual to provide
detailed programs. For more detailed information on programming in general, refer to the Paper-Tape Software
Programming Handbook, DEC-II-GGPB-D.
This chapter of the manual is divided into four major portions: device registers, interrupts, programming note,
and program example.

4.2 DEVICE REGISTERS
All software control of the TM 11 DECmagtape System is performed by means of six device registers within the
controller. These registers have been assigned bus addresses and can be read or loaded using any PDP-II instruction that refers to their address. The six device registers and associated addresses are listed in Table 4-1. Note
that these addresses can be changed by altering the jumpers on the M 105 Address Selector Module. However,
any DEC programs that refer to these addresses must also be modified accordingly if the jumpers are changed.
Figures 4-1 through 4-6 show the bit assignments within the six device registers. Except in the case of the data
buffer register, the "unused" and "load only" bits are always read as Os. Loading "unused" or "read only" bits
has no effect on the bit position.
The mnemonic INIT refers to the initialization signal issued by the processor. Initialization is caused by one of
the following: issuing a programmed RESET instruction; depressing the START switch on the processor console;
or occurrence of a power-up or power-down condition of either the processor power supply or the controller
power supply.
The INIT signal clears the entire system; however, the INIT signal produced by a RESET instruction does not
clear the processor. Clearing only the TMII Controller and the TUIO tape units can be accomplished by either
using the CLEAR switch on the TMll Maintenance Panel or by loading a 1 into bit 12 (POWER CLEAR) of the
command.register (MTC).
NOTE
INIT and POWER CLEAR deselect the current tape
unit and select tape unit O. Also, a rewind operation
in progress continues to the load point.

4-1

Table 4-1
Standard Device Register Assignments
Register
Status Register
Command Register
Byte Record Counter
Current Memory Address Register
Data Buffer Register
TV 10 Read Lines

Mnemonic*

Address

MTS
MTC
MTBRC
MTCMA
MTD
MTRD

772520
772522
772524
772526
772530
772532

*First two letters of mnemonic (MT) refer to magnetic tape control; the remaining letters represent the mnemonic of a specific register.

4.2.1 Status Register (MTS)

1/-0'130

Figure 4-1 Status Register (MTS) Bit Assignments
Meaning and Operation

Bit

ILC - illegal command bit. Indicates an illegal command. This bit is set whenever one of the following illegal commands occur:
a.

Any DATO or DATOB transfer to the command register (MTC)
during tape operation (CU RDY bit clear). The register cannot
accept a new command while in the process of executing another
command.

A write, write end-of-file, or write with extended interrecord gap
(command register functions 2, 3, and 6, respectively), when the
WRL (write lock) bit is set. Writing is inhibited with WRL set,
and write commands are illegal.

Any command to a tape unit that has its SELR bit clear is illegal,
because SELR clear indicates that the unit is not on-line.

Any time the SELR bit becomes 0 during any operation except
off-line, it sets the ILC bit, because no command can be issued
to a unit that is not on-line.

If any of the illegal commands listed in a. through c. above occur, the command

IS loaded into the command register.
In all of the above cases, the ILC bit and the ERR bit (bit 15 in the command
register) are set simultaneously.
Cleared by IN IT or by the GO pulse to the tape unit.

4-2

Bit

Meaning and Operation

EOF - end-of-file bit, used to indicate that the tape has reached the end of the
file. An end-of-file (EOF) character is detected during a read, space forward,
or space reverse operation. During the read or space forward operation, the
EOF bit is set when the LPC character following the EOF character is read.
During a space reverse operation, the EOF bit is set when the EOF character
following its LPC character is read. The ERR bit (bit 15 in the command
register) is set when the LPC character following the EOF character is
. detected. It is also set by a WRITE EOF command.
The EOF bit is set only by the TUIO logic; it is cleared by INIT or by the GO
pulse to the tape unit.
The EOF character is loaded into memory during read operations.

eRE - cyclic redundancy error bit. A cyclic redundancy error can be detected

during either a read or write operation. This check compares the CRC character,
written on a 9-channel tape during a write or a write-with-extended-IRG operation, with the CRC character generated during a read operatis>n.
If the two CRC characters are not the same, the CReE from the tape unit be~
comes a I, forcing the CRE bit to a 1. The ERR bit in the command register,
however, is not set until the LPC character is detected.
Cleared by INIT or by the GO pulse to the tape unit.
12

PAE - parity error bit. When set, this bit indicates that a parity error exists.
The PAE bit is the logical OR of both lateral and longitudinal parity errors.
A lateral parity error is indicated on any character in a record; a longitudinal
parity error occurs only after the LPC is detected.
.'

A lateral parity error does not affect the transfer of data. In other words, the
entire record is transferred to the tape during a wri~e operation or transferred
into memory during a read operation.
Both lateral and longitudinal parity errors are detected during read, write, and
write-with-extended-IRG operations. The entire record is checked, including
the CRC and LPC characters.
Longitudinal parity occurs when an odd number of I s is detected on any channel in the record. Lateral parity error occurs when an even number of I s is
detected on any character, provided the PEVN bit (bit 11 in the command
register) is clear, or if an odd number of 1s is detected when the PEVN bit is set.
When a parity error occurs, PAE is set, and the ERR bit (bit 15 in the command
register) is set after the LPC character has been detected.
Cleared by INIT or by the GO pulse to the tape unit.
11

BGL - bus grant late bit. If the controller issues a request for the bus and does
not receive a bus grant before it must issue another bus request for the following
tape character, a bus grant late error occurs.
This error condition is tested only for NPRs (non-processor requests). The BGL
bit is set if an NPR bus request is not honored before the controller receives a
WRS pulse for a write operation or an RDS pulse for a read operation.

4-3

Bit
11 (cont)

Meaning and Operation
The BGL bit and the ERR bit (bit 15 in the MTC) are set simultaneously, halting
the operation.
If the BGL error occurred during a write or write-with-extended-IRG operation,
the controller does not send the WDR signal to the master tape unit to allow the
master tape unit to write the CRC and LPC characters on the tape.

Cleared by INIT or by the GO pulse to the tape unit.
10

EDT - end-of-tape bit. The EaT bit is set as soon as the EaT marker is detected,
when the tape is moving in the forward direction. It is cleared as soon as the EaT
marker is detected, when the tape is moving in the reverse direction.
The EaT is an error condition if the tape is moving forward. Therefore, when
EaT is set, ERR bit is also set when the LPC character is read.
Cleared by tape transport he"ad passing over EaT marker when tape is moving
in the reverse direction.

RLE - record length error bit. The record length error is tested only during read
operations. An error is indicated as soon as the byte record counter (MTBRC)
attempts to increment beyond O.
When a record length error occurs, the RLE bit is set, incrementation of the
MTBRC and the current memory address register (MTCMA) ceases, and the
ERR bit is set when the LPC character is read.
The CU RDY (bit 07 of the command register) remains cleared until the LPC
character is read at which time CU RDY is set.
Cleared by INIT or by the GO pulse to the tape unit.
If the exact record length is desired following the occurrence of a record length
error, it can be found by setting the MTBRC to a value so large as not to generate
an RLE and re-reading the record. Record length can be derived by subtracting
the current value of the MTBRC from its initial setting.

BTE - bad tape error bit. A bad tape error occurs when a character is detected
(RDS pulse) during the gap shutdown or settle down period for any tape
function except rewind.
During write, write EOF, or write-with-extended-IRG operations, a bad tape
error sets both the BTE and ERR bits immediately on detecting the error.
During both read and space forward or space reverse operations, the BTE bit
is set immediately on detection of bad tape.
During a read operation, the MTBRC increments continuously, and words are
read into memory until the MTBRC overflows. During a space operation, the
MTBRC stops incrementing as soon as BTE occurs. When BTE is discovered,
the tape unit stops, regardless of the state of the MTBRC.
Because it it not possible to artificially generate bad tape, bad tape may be indicated by setting the CU RDY bit prematurely, thereby producing the gap
shutdown period while the data is still being read. The CU RDY bit is set by
loading a I into bit 13 of the MTRD. If bit 13 of the MTRD is set during a
record for either a read or write operation, a bad tape error indication occurs.
Cleared by INIT or GO.

4-4

Bit

Meaning and Operation

NXM - non-existent memory bit. This error condition occurs when the controller is bus master during NPR transfers and does not receive an SSYN response
within lOllS after asserting MSYN.
The NXM bit and the ERR bit are set simultaneously, halting the operation.
Cleared by IN IT or by the GO pulse to the tape unit.

SELR - select remote bit. The SELR bit is set when the tape unit has been
properly selected. The SELR bit is 0 if the tape umt that is addressed does
not exist (UNIT SELECT setting does not correspond to SEL bits), if the
selected tape unit is off-line (ON-LINE/OFF-LINE switch set to OFF-LINE),
or if the tape unit power is off.

BOT - beginning-of-tape bit. The BOT bit is set as soon as the BOT marker
is detected. When BOT is set, it has no effect on the ERR bit. The BOT bit
remains cleared whenever the BOT marker is not being read.
This bit is set and cleared only by the TU I O.

7CH - 7-channel bit. This bit is cleared or set by the TUIO to indicate whether
a 7-channel or 9-channel tape is being used.
When 7CH bit is set, it indicates a 7-channel tape; when it is clear, it indicates
a 9-channel tape.
The 7CH bit is also used in conjunction with the DEN 8 and DEN 5 bits in the
command register to cause the core dump mode of operation. When the 7CH,
DEN 8, and DEN 5 bits are all set, thecore dump mode of operation is used.

SDWN - settle down bit. The settling down period is provided to allow the
tape to fully stop prior to starting a new operation. This settling down period
sets the SDWN bit. When the tape unit stops, SDWN is cleared, and the tape
unit ready (TUR) bit is set.
During a tape reverse operation (this does not include rewind operations), the
gap shutdown period begins immediately after the first gap encountered after
spacing over a record.
When the controller receives a command during the gap shutdown period, it
executes the command at the start of the settling down period unless the new
command is for the tape unit issuing the SDWN period, and the new command
is opposite to the current direction of tape motion. If both of these conditions
occur, the controller accepts the new command only if SDWN is cleared.
The controller accepts all commands received while the CU RDY bit is set,
including commands received during the tape settling down period. Thus,
commands received during the settling down period are buffered and transmitted to the master tape transport at the end of the settling down period.

WRL - write lock bit. The write lock bit is under control of the master tape
transport. When set, it prevents the controller from writing information on
the tape.

4-5

Bit

Meaning and Operation

RWS - rewind status bit. This bit is under control of the master tape unit.
I t is set at the start of a rewind operation and clears as soon as the rewind
sequence is complete.

TUR - tape unit ready bit. This bit is under control ~f the master tape transport. Whenever the selected tape unit is being ,:!sed (such as rewind), this bit
is cleared. When the tape unit is stopped and ready to receive a new command,
the master tape transport sets the TUR bit.
NOTE
register bits 00 - 05 are cleared or set by the
master tape transport, not the controller.
St~tus

4.2.2 Command Register (MTC)

11-0431

Figure 4-2 Command Register (MTC) Bit Assignments

Bit
15

Meaning and Operation
ERR - indicates an error condition that is the inclusive OR of all error conditions
(bits 15 - 07 in the Status Register, MTS). Causes an interrupt if enabled (see bit
06). The ERR bit is not set for some errors until the longitudinal parity check
(LPC) character is read, in order to allow the current operation to be completed.
Specific error conditions are described in the Status Register bit assignments
(see Figure 4-1).
When ERR is set, it sets bit 07 (CU RDY). Cleared by INIT or by the next
GO command (bit 00).

DEN 8 - this bit, in conjunction with bit 13, selects the bit packing density of
the tape. These combinations are shown below. Note that this bit, in conjunction with DEN 5 and 7CH in the MTS, can be used to select the core dump mode
(refer to Paragraph 5.8.2.2) for 7-channel tape.
Bit 14
(DEN 8)

Bit 13
(DEN 5)

o
o

Density
(bits/inch)
200}
556
800
800

4-6

7-channel tape
9-channel tape

Bit

Meaning and Operation

DEN 5 - this bit, in conjunction with bit 14, selects the bit packing density of
the tape. See bit 14 above for combinations.

PWR CLR - when a 1 is loaded into this bit position, it clears the controller logic
and all tape units. This bit becomes a I for I J.LS during a processor DATO cycle,
provided the corresponding bit on the bus is a 1. Always read by processor as a o.

PEVN - this is the even parity bit. This bit is set whenever the selected
tape unit is to write or read even lateral parity on or from the tape. The bit
is 0 whenever the selected tape unit is to write or read odd lateral parity on
or from the tape.
A search for parity error is made whenever the tape moves. The controller ignores
parity errors during space forward, space reverse, or rewind operations.
Cleared by INIT or by loading with a O.

10-08

SEL - these three unit select bits specify the number of the tape unit that is to
function as the unit under program control. These three bits (SEL 2, SEL I,
and SEL 0) are set or cleared to represent an octal code that corresponds to the
unit number of the tape unit to be used. The tape unit number is selected by
the UNIT SELECT thumb wheel switch on the tape transport.
Cleared by IN IT ; cleared by loading with a O.

CU ROY - when set, indicates that the TMII Controller is ready to receive a
new command. This bit is set at the end of a tape operation (indicating that a
new operation can be started) and is cleared at the beginning of a tape operation
(indicating that the controller is not ready for new commands). Refer to
Paragraph 4.4.1 for CU RDY operation during a rewind sequence.
This bit is also set (indicating CU RDY) whenever ERR (bit 15) is set or
whenever INIT is generated.

INT ENB - interrupt enable bit. This bit, when set, allows an interrupt to
occur, provided either CU RDY (bit 07) or ERR (bit 15) is set. With INT
ENB set, a REWIND command can cause two interrupts - one at initiation
and one at completion.
An interrupt also occurs whenever an instruction sets the INT ENB bit
but does not set the GO bit (bit 00). Interrupts are described in Paragraph 4.3.
Cleared by INIT; cleared by loading with a O.

ADRS BIT 17 - extended bus address bit 17. Used to specify address line 17
in direct memory transfers. Increments with the Current Memory Address
Register (MTCMA). Cleared by INIT.

AORS BIT 16 - extended bus address bit 16. Function is the same as
ADRS BIT 17 (bit 05 above).

4-7

Meaning and Operation

Bit

03-01

FUNCTION - these bits specify a command to be performed by the selected
tape unit. These functions are:

Octal No.
0

2
3
4
5
6
7

Function Bits
03 02 01
0
0
0
0

0
0

1
0
0

0
I

Function
Off-line
Read
Write
Write end of file
Space forward
Space reverse
Write with extended IRG
Rewind

All function bits cleared by INIT. Table 5-1 describes each function.
GO - loaded with a 1 from the bus to initiate the function selected. Clears
CU RDY bit.

Cleared when GO pulse is sent to tape transport. Normal time duration of bit
is 1 p,s, but this time may extend to as long as 10 ms if the bit is set during the
gap shutdown or settling down period. The time could be several minutes in the
case where the bit is loaded for a tape unit, i.e., in the process of rewinding.
Also cleared by INIT or cleared whenever ILC in the status register is set.
4.2.3 Byte Record Counter (MTBRC)
00

15
2's

COMPLEMENT OF NUMBER OF BYTES

(OR RECORDS) TO BE COUNTED
11-0432

Figure 4-3 Byte Record Counter (MTBRC) Bit Assignments

Bit
15-00

Meaning and Operation
Contains the 2's complement of the number of bytes or records to be transferred. The desired value is loaded by the program on a processor DATa.
Cleared by INIT. Increments by I after each memory access.
The byte record counter (MTBRC) is a 16-bit binary counter used to count
bytes in a read or write operation and used to count records in space forward
or reverse operations.
When used in a write or write-with-extended-IRG operation, this register is
set by the program to the 2's complement of the number of bytes to be
written on the tape. After the last byte of the record has been strobed from
memory, the MTBRC becomes O. Thus, when the next write strobe signal
is received from the master tape transport, the controller lowers the write
data ready line to indicate to the master transport that there are no more data
characters in the record.

4-8

Bit

Meaning and Operation

15-00 (cont)

When used in a read operation, the MTBRC is set to a number equal to or greater
than the 2's complement of the number of words to be loaded into memory. A
record length error, which occurs for long records only, occurs whenevera read
pulse is generated after the MTBRC is at O. Neither the CRC or LPC 'ctra~acter is
loaded into memory during a read operation, although both characters are
checked for parity errors.
When used in a space forward or space reverse operation, the MTBRC is loaded
with the 2's complement of the number of records to be spaced. The counter is
incremented by I at LPC time, regardless of tape direction.

4.2.4 Current Memory Address Register (MTCMA)
00

15
BUS ADDRESS
11- 0433

Figure 4-4 Current Memory Address Register (MTCMA) Bit Assignments
Bit

15-01

Meaning and Operation
These bits specify the bus or memory address to or from which data is to be transferred during write or read operations. Only bits 01-15 of the MTCMA are accessible by the program, although bits 00-15 participate in NPR Transfers. Bit 00 always starts in the cleared or even byte state because all NPR transfers access even
boundaries for a starting byte address. Therefore, MTCMA must be initially loaded
with an even address. The MTCMA contains 16 of the possible 18 memory address
bits. The remaining two bits ( 16 and 17) are part of the command register.
Before issuing a command, the program loads the MTCMA with the memory address that is to receive the first byte of data (read operation) or with the memory
address from which the first byte is. to be taken (write operation). After each
memory access (read or write), the MTCMA is immediately incremented by 1
(the next byte boundary), Therefore, at any given time, the MTCMA points to
the next memory byte address that is to be accessed. On completion of the
record transfer, the MTCMA points to the address plus 1 of the last character
in the record.
If a bus grant late (BGL) or non-existent memory (NXM) error occurs, the
MTCMA contains the address of the location in which the failure occurred.
If an 18-bit memory address is required, the program loads the appropriate address
into bits 01-15 of the MTCMA and into extended address bits 16 and 17 of the
command register. The extended address bits are a logical extension to the
MTCMA register and participate in any required incrementation.

4.2.5 Data Buffer Register (MTD)
00
DATA (7-CHANNEL TAPE)
11-('434

Figure 4-5 Data Buffer Register (MTD) Bit Assignments

4-9

Bit

Meaning and Operation

15-09
(not shown)

Correspond to bits 07-01 respectively on a processor DATI cycle.
Example: Bit 15 = bit 7, bit 14 = bit 6, etc.

Correspond to the parity bit on the magnetic tape. During a processor read operation, this bit is stored in memory; during NPR operations, this bit is read by the
controller but not loaded into memory. During operation of a 9-channel tape
unit, this bit is valid only after the CRC character has been read, provided bit 14
of the MTRD is a 1.
NOTE
The parity bit is generated by the TVtO master tape
transport, it is not generated by the controller. However, the polarity of the parity bit (odd or even) is
detennined by the PEVN bit in the command register.
08

9 TRACK TAPEFULL 8-81T BYTES ARE RECORDED ON TAPE.
15

7 TRACK TAPEONLY 6 BITS OF EACH 8-BIT BYTE ARE RECORDED
ON TAPE.BITS 6,7,14, AND 15 ARE NOT USED.
15

12
D

07
B

00
A

7 TRACK TAPE (CORE DUMP)FULL 8-BIT BYTES ARE RECORDED ON TAPE
BY USING TWO 4-BIT CHARACTERS
(REFER TO PARAGRAPH 5.8.6).

READ/WRITE
HEAD

11- 2061

Figure 4-6 Relationship Between Tape Characters and Memory Byte Characters

07-00

During read operations, these bits are used for temporary storage of characters
read from tape prior to loading into memory. During write operations, these
bits are used for temporary storage of data from memory before writing on tape.
During read operations, the LPC character enters the data buffer when bit 14 of
the address location for the TVI 0 read lines is a 1; the LPC character is prevented from entering the data buffer when bit 14 is a O. Thus, after reading a
9-channel tape, the data buffer contains an LPC character (if bit 14 is a 1) or a

4-10

Bit
07-00 (cont)

Meaning and Operation
CRC character (if bit 14 is a 0). After reading a 7-channel tape, the data buffer
contains either the LPC character (if bit 14 is a 1) or the last data character (if
bit 14 is a 0). After reading an EOF character, the data buffer contains either
all Os (bit 14 is a 1) or the EOF character (bit 14 is a 0).
The data buffer can store only bytes; therefore, two bus cycles are required to
transfer a word. During NPR operation the data bits are written into or read
from alternate low and high byte positions. The relationship between tape
characters and high and low memory byte characters is shown in Figure 4-6.

4.2.6 TUIO Read Lines (MTRD)
09

DATA

UNUSED

11-0435

Figure 4-7 TVIO Read Line (MTRD) Bit Assignments
Bit

Meaning and Operation

TIMER - the timer bit is used for diagnostic purposes by measuring the time
duration of the tape operations. The timer signal is a 100 ps signal with a 50%
duty cycle and is generated by the controller. It is read as bit 15 in the memory
location reserved for the TV 10 read data lines. Read only bit.

CHAR. SEL. - this bit is used to select the last character of a record that is to
be loaded into the data buffer. Read/write bit. Selection is as follows:
7-channel
set
clear

9-channel

LPC character
last data character

LPC character
CRC character

BTE GEN. - bad tape error generator bit. Actually, bad tape cannot be
artificially generated. When set, this bit sets the CU RDY bit. With CV RDY
set, a premature gap shutdown is generated, which produces a bad tape error
indication when data is read during this period. Write only bit.

GAP SHUTDOWN - read only bit. When set, indicates a gap shutdown period.

11-09

Unused.

PARITY - corresponds to the parity bit read from the tape by the master tape
transport. Used in conjunction with bits 07 -00 to indicate a longitudinal parity
error. After a read or write operation, bits 08-00 should all be O. If one or more
of these bits remains a 1 after the operation is complete, it indicates a longitudinal
parity error. The bit position containing the 1 indicates the tape channel containing the error. Read only bit.

07-00

DATA - these bit positions contain information read from the magnetic tape
transport. After these positions are read by the processor, all bit positions clear
unless a parity error exists.
Bits 07-00 in the read lines correspond to tape channels 00-07, respectively.
Read only bits.

4-11

4.3 INTERR UPTS
The TM 11 Controller uses NPR or BR interrupts to gain control of the bus in order to perform data transfers or
to cause a vectored interrupt, thereby causing a branch to a handling routine. The NPR requests are used for
direct memory access, whenever it is desired to transfer data between memory and the data buffer register without processor intervention. The BR requests are made when processor servicing is required for completed
operations or error conditions.
4.3.1 NPR Requests
The TM II Controller issues an NPR request whenever it is necessary to transfer data between memory and the
data buffer register. During a read operation, the direction of transfer is from the data buffer to the core memory. The RDS pulse (read strobe, from master tape transport to controller), which is used to strobe data from
the tape transport into the data buffer register, generates the NPR request. When the request is granted, the
TMII Controller performs a DATOB bus cycle and transfers information from the data buffer into memory.
During a write (or write-with-extended-IRG) operation, the NPR request is generated by the write strobe (WRS)
pulse from the processor. When the request is granted, the controller performs a DATI bus cycle and transfers a
byte from core memory into the data buffer register.
During both read and write operations, the address in memory that data is read from or loaded into is determined
by the value in the current memory address register (MTCMA).
4.3.2 BR Requests
A BR interrupt can occur only if the interrupt enable (INT ENB) bit in the command register is set. With INT
ENB set, setting either the CU RDY or ERR bit in the command register, or completing a rewind operation
initiates an interrupt request.
When CU RDY is set, it indicates that the controller is ready to perform another command.
When ERR is set, it indicates that some type of error condition exists. In this case, an interrupt is used to cause
the program to branch to an error handling routine.
If a function command is issued with the GO bit cleared and INT ENB set, an interrupt is initiated.
If the selected tape unit (as indicated by the SEL bits in the command register) completes the rewind operation
before a new command to that unit is received and INT ENB is set, an interrupt is initiated.
If the interrupt is enabled (INT ENB set) and selection of the tape unit is not changed (as indicated by the SEL

bits), then a rewind command causes two interrupts: an interrupt when the rewind function begins, and an
interrupt when the tape unit completes the rewind function. If, however, the tape unit is already at the BOT
marker when rewind is issued, only one interrupt occurs.
The interrupt priority level is BRS, and the interrupt vector address is 224. Note that the priority level can be
changed by the priority chip on the G736 Module, and the vector address can be changed by jumpers on the
M7821 Interrupt Control. However, any DEC programs or other software referring to the standard level or address must also be changed if the jumpers are changed.
4.4 PROGRAMMING NOTES

In normal programming practice no attempt should be made to modify one record in the middle of a file. This
practice could result in overwriting the boundary of the record and destroying part of the next record. Also, a
read operation should never directly follow a write operation without at least one intervening tape move operation. This prevents running off the reel if the previous operation involved the last record on the tape. If it is

4-12

desired to read a record that was just written, a space reverse command should be issued before the read command.
New commands are issued only when CU RDY is set, which is true after interrupts.
Because of a TM 11 logic restriction, all software READ/WRITE buffer areas used by TM 11 NPR transfers must
start on even byte boundaries.
Attempting to write an all zero character with even parity on a 7-track or 9-track tape unit causes the zero character to be converted to a tape character of twenty (20). When reading this character from tape a twenty (20) is
read instead of a zero.
When changing unit numbers in multi-transport software, the status bits (such as WRITE LOCK) are not switched
from the old transport to the newly selected one at the time the command is loaded. The status bits are those
of the old transport until the interrecord gap of the previous comma~d has bee~ written. Therefore, valid status
bits from the new transport are not present until SDWN is a 1 (asserted). Because SDWN does not cause an
inteuupt, the software must wait in a loop for approximately two milliseconds or exit the routine and re-enter
as a function of a time clock.
The standard reel capacity for industry compatible magtape units is 2400 feet, marker to marker. However,
less tape may be used, such as in the mini-magtape reels. ASCII standards provide for a 25 foot trailer following
the end-of-tape marker. This allows approximately 10 feet of writing space after passing EaT. Care should be
taken when attempting to write past the EaT marker if the operator is not familiar with the tape that he is
working with, because after a tape has been used, the reflective markers are often changed, pOSSIbly decreasing
the length of the standard 25 foot trailer.
Because the physical displacement of the heads differ between 7-channel and 9-channel drives, records written
on one cannot be read by the other. However, a tape that is recorded on one can be re-recorded by the other,
providing you begin at the load point.
TUIO's and TU16's can be used on the same system; however, due to the fact that the TUI0 is a Unibus device
and the TU 16 is a Massbus device, they may not be used on the same controller.
If two drives are sharing one controller, care should be taken not to allow both drives to have the same unit
number selected on the thumbwheels. If they are both set to the same number and a command is issued, they
will both attempt to respond and data transfers will become totally confused.
The industry standard packing density for 9-channel drives is 800 bpi, however, 9-channel drives may be
recorded at 200, 556 or 800 bpi, providing the data is read back at the same rate.
A backspace or REWIND command issued while the tape is at the load point will cause an immediate interrupt.
4.4.1 Rewind Operation
Assume drive 0 is to be rewound. The command to rewind drive 0 is issued to the controller. At this time the
master tape unit asserts bit 1 (RWS) in the status register. If bit 6 (INT ENB) in the command register was set
at the start of the rewind operation, an interrupt occurs from the TM 11 controller as soon as bit 7 (CU RDY)
of the command register has been set by RWS. This informs the program that the controller is ready to accept
a new command. By testing bit 1 (RWS) in the status register, the program can determine if this interrupt was
issued as a result of drive a completing its rewind operation or just beginning it.
When the reflective marker, signifying BOT, is sensed, bit 5 (BOT) is asserted in the status register only for the
duration of time that the reflective marker is being read. Tape motion does not stop at this time.

4-13

Drive 0, still moving in the reverse direction, passes over the reflective marker, reverses its direction, and proceeds in the forward direction back to the load point. Upon sensing the reflective marker while proceeding in
the forward direction, drive 0 halts tape motion, asserts bit 3 (SDWN) allowing the tape to fully deskew, and
then sets bit 0 (TUR) in the status register.
An interrupt is issued coincident with bit 0 (TUR) being asserted in the status register, providing the following
conditions have been met.
1.

Bit 6 (INT ENB) in the command register is set,

The drive has not been deselected by changing the status of bits 10-8 in the command register since
issuing the REWIND command, and

No new commands are stored in the controller awaiting execution. If a new command is being stored,
the next interrupt will be after that command's completion and no rewind complete interrupt will
occur.

If multiple transports are used, it is not necessary to wait for a REWIND command to be completed on one
transport before switching to another. After a REWIND is issued, another transport can be switched to as
soon as RWS is set.
When operations on the second transport have been completed, a switch to the rewinding transport can be made
as soon as SDWN or TUR is true on the second transport (so the status bits will be from the rewinding unit).
Only the unit select bits in the command register have to be changed to the unit that is rewinding to get its
status. If the rewind is complete when the unit is selected, TUR is set in the status register. If the RWS bit is
still set, the software can either work on another transport or load the next command to be executed in
bits 1-3 of the command register where it is buffered until the rewind is completed. If INT ENB is set at this
time, the completion of the buffered command causes an interrupt to occur. A REWIND command may take
from 3 to 5 minutes to complete.

4-14

4.4.2 New Drive Selection
Figure 4-8 is a flow chart for new drive selection.

START NEW
OPERATION

YES

ERROR

LOAD NEW
COMMAND
AND INT. ENB.

11·:;!51:;!

Figure 4-8 New Drive Selection Flowchart

4.4.3 Error Handling
4.4.3.1 Write Operations
I.

ILC •

Illegal Command

If SELR (bit 6 of MTS) is not set to a I, or WRL (bit 2 of MTS) is set to aI, then operator

intervention is required to ensure that the drive to be used is properly selected and is not
write locked.
•

If SELR (bit 6 of MTS) is set to a I and WRL (bit 2 of MTS) is not set to aI, then a command

has been issued while CU RDY (bit 7 of MTC) was cleared. Try the operation again, ensuring
first that CU RDY is set before issuing a new command.

4-15

EOF -

End of File

N/ A

CRE -

Cyclic Redundancy error
Backspace and try operation again with extended IRG.

PAE -

Parity error
Backspace and try operation again with extended IRG.

BGL -

Bus grant late
Backspace and try operation N times.

EOT -

End of tape
The reflective marker signifying the end of tape has been passed. Operations past this point
are not illegal, however, they are not recommended unless the programmer is familiar with
the tape being used and is knowledgable about the length of tape existing past the EOT
marker. Conducting any write operations past the EOT marker leaves the programmer open
to the possibility of running the tape off of the reel.

RLE -

Record length error

BTE -

Bad tape error
Regain a known tape position and try the operation again with extended IRG.

N/A

NOTE
A known tape position refers to BOT, header records,
or EOF marks.
9.

NXM- Non-existent memory
Resolve the memory discrepancy and try the operation again.

4.4.3.2 Read Operations
1.

ILC -

Illegal Command

•

If SELR (bit 6 of. MTS) is not set, then operator intervention is required to ensure that the drive
to be used is properly selected.

•

If SELR (bit 6 of MTS) is set, then a command has been issued while CU RDY (bit 7 of MTC)
was cleared. Try the operation again en~uring that CU RDY is set prior to issuing the new
command.

EOF-

CRE- Cyclic Redundancy error
Backspace and try the operation N times.

PAE- Parity error
Backspace and try the operation N times.

BGL-

End of file
The characters signifying the end of a file have been read.

Bus grant late
Backspace and try the operation N times.

4-16

EOT -

End of tape
The reflective marker signifying the end of tape has been passed. Continue only if it is
certain that an EOF mark exists after the EOT marker, or the tape will run off of the reel.

RLE -

Record length error
Reset the MTBRC to a value that is equal to or greater than the number of bytes in the
record, backspace, and try the operation again.

BTE -

Bad tape error
Regain a known tape position and try the operation again. If, after doing so, the condition
still persists, the data from the failing point to the next known tape position is lost.

NXM- Non-existent memory
Resolve the memory location discrepancy and try the operation again.

4.4.3.3 Write End of File Operation
All Errors
This operation should have a software timer because it either performs its function correctly or it enters
a run-away condition and runs the tape off the reel. If this condition is sensed after a few seconds,
recovery is as follows:
•

Issue a POWER CLEAR to stop tape motion.

•

Regain a known tape position and try the operation again.

4.4.3.4 Spacing Operations
1.

ILC -

Illegal command
Same as read operation.

EOF -

End of file
The characters signifying the end of a file have been read. Detection of the EOF marks stops
a spacing operation even if the MTBRC is not equal to zero'.

EOT -

End of tape
Same as read operation.

BTE -

Bad tape error
Regain a known tape position and try N times.

4.4.3.5 Write With Extended IRG Operation
Same as write operation.

4.4.3.6 Rewind Operation
Once a rewind operation is started, it continues until complete, regardless of errors or unit deselection.
4.5 PROGRAM EXAMPLE
The following program example is used to write a 1ODD-byte record,· backspace, read the record, and compare
data.

4-17

MT8RC:;17~524

MTCM.,;172526

~"1"00
~01~f2I0

0~5"67

001004
f2J0"0U.'l
"01.,,12
001016
"01020
0.01026
0011"34

lk'5767

.=1~0fZ!

176"~0
~6"i2l05

fiH'l1~~6

1210315

"lZll~50

"'12767
71 12167
105767
100315

177777

~12767

~flJ3120

"12767
("12761
1.05767
100375

1162130
(1JbIZl0r!l3

2127e'0

00115Z
003120

0.0U170
0"1072
00j,1 f2J .0
001106
0211114
0"1120

17151?Jk?

17147[0
171460

111454

105761

MTC
"1TC

ecc

"'1TS
,-4

lIS TAPE UNIT

MOV

#WBUF,MTCHA

~OV

*~1~~0,,~T~RC

MOV
TST8

M'T'C

MTCMA WITH BurrER AREA TC BE WRITTEN
eYTE COU~T
ISELECT UNIT #~, 8~~ BPI. WRITE, ISSUE GO
lIS rO~TRO~ UNrT R~AOY, INDICATING COMPL~T10N OF
J~~, WAIT

8P~
R(JR

1'1'11'2
0.01150

T~T9

r.CR

171516
171512

0.010~2

0.010~6
001~64

123315
e!12767
:"112767
r12767

8PL,

~~0013

1'144~
11143~

.-4

#6~~05,MTC

,_4

,RECORD WRITTEN, NOW 8ACKS~ACE
MOV
#-l,MTBRC

171432

MOV

#6~013,MTC

TSTB

MTC

8Pl.

1",4

JNOW READ RECORD

1714~~

171426
17141Q
1114"'~

MOV
MOV
MOV
T5T8

e22021

0011~0

~2~027

001,1~4

~02712

8~!

0011~6

~0a0~0

0.011 5 0

N3t'10Q!0
("0312.0

W8Ul=" I

HA~T
C'I

01213120

~000~0

RBUFI

!21

1!014~1

CHHHH'10

?,000~1

003120

JCLEAR COMMA~D REGISTER, ALSO SELECTS UNIT
JIS CONTROL. UNIT READY?
JNC. WAIT

READY?

IN~. WAIT
Jl~ITlALI~E

'INITIALI~~

IINITIAL,lt~ BYTE COUNT T~ BACKSPACE 1 RECORD
,ISSUE BACKSPAeE COMMAND
115 CONTROL. UNIT R~ADY, tN~IeATING COMPL,ETION OF
JNO. WAIT

W~ITE?

8AC~SPACE?

IINITIAL,llE MTCM. WITH 8UrrE~ AREA TO RE REA~ !NTO
,lNITIALIlE RYTE COUNT
#6~~03,MTC
,sr~rcT UNIT #~, a~~ BPI, READ. ISSUE GO
MTC
115 CONTRO~ UNIT READY, iNDICATING COMPLElrON OF REAO?
~pC
,.4
JN~. WAIT
ICOMPARE DATA ~EAD WITH DATA WRITTrN
MOV
jWBUF,%0
JU~E RrGIST[RS 0,1 AS Bu~rrR P~lNTERS FOR COMPARISON
MOV
*R8UF,~1
eMP
(~)+,(l)+
ell
iIS DA'A WRITTEN = DATA ~EAD?
8E.Q
,+4Ives
HA~T
INO. H~VE DATA ERROR
CMP
~~,#W8~F+l~0~~
IrtNIs~ED COMPARISON or ~urFER'

flJ01122
001126
flJ01132
0211134
00'-136

(;',127~1

~EGlST[R

JWRITE RECORD

10~315

"'06061

,STATUS REGISTER
IC~MMAND REGISTER
,8VTr ~ECORD C~UNTER
,CURPENT MEMORY ADORESS

MTS=172520
MTC=172522

172520
172522
172524
172526

1 : 1oI

#RBU~,MTCMA

j~1~~0!,MTBRC

Cl
8UF+UH}I1l,
,END

I~O

Jvrs,

rXAMP~E COMPLETED
,WRITE BurrER BEGINS HERE

IRrAn

~UrFER

BEGINS

~ERE

CHAPTER 5
THEORY OF OPERATION

5.1 INTRODUCTION

This chapter provides a detailed description of the TM 11 Controller and consists of three major parts: functional
description of overall controller operation, block diagram description of major components, and detailed description covering controller logic circuits. The discussions in this chapter are supported by a complete set of engineering drawings located in a companion volume entitled, TM 11 DECmagtape System, Engineering Drawings.
The TMl1 Controller may be divided into seven functional areas: selection logic, bus control logic, register logic,
tape control logic, read/write logic, error logic, and control panel logic. Parity logic is part of the Master Tape
Transport and is, therefore, only covered in general in subsequent discussions. The purpose of each of the controller functional units is as follows:
Selection Logic

Determines if the controller has been selected as a bus slave device, and
what type of operation (read or write) has been selected. Permits selection of one of six internal registers for use and determines if the register
is to perform an input or output operation.

Bus Control Logic

Permits the controller to gain bus control either by means of an NPR
for transferring data or by means of a programmed interrupt to req uest
service by the program because an error condition exists, because the
controller is ready to perfonn a new operation, or because the controller is ready to make a direct memory access transfer (NPR transfer).

Six internal registers, addressable by the program, provide data transfer
functions, command and control functions, and status monitoring functions for the TM 11 Controller.

Tape Control Logic

Controls selection of tape unit, direction of tape travel (forward,
reverse), and function to be perfonned such as rewind, write, read,
space forward, and space reverse.

Read/Write Logic

Controls assembly, disassembly, and transfer of data between the magnetic tape and the Unibus. Counts number of words in transfer and
keeps track of current bus address.

Error Logic

Monitors controller operation and provides an indication of any error
condition that arises. Stops the operation and issues an interrupt request for most error conditions.

Control Panel Logic

Provides signals that light indicators on the controller maintenance
panel; controls operation of the CLEAR switch.

5-1

5.2 TAPE FORMAT
The tape format used in the TMll DEC magtape System is identical to industry standard 7- and 9-channel tape
formats. It is assumed that the reader is familiar with standard magnetic tape formats. If not, a more thorough
explanation is presented in Chapter 1 of the TU10 DECmagtape Manual, DEC-OO-TUIOM-D.
Each character frame in a 7-channel tape (see Figure 5-1) consists of six character bits (B, A, 8, 4, 2, 1) in descending order of significance. The parity bit, or check bit (C), is the seventh bit and is set or cleared by the transport
write head. One byte of a PDP-II word corresponds to one tape character. However, because one byte contains
eight bits and a tape character contains only six data bits, two bits within each byte are not used. During a read
operation, the extra bits are forced to 0; during a write operation, the bits remained unchanged. During the core
dump mode of operation, one PDP-II byte corresponds to two tape characters. Thus, all bits within the byte are
used; however, the two most significant bits on the tape are not used.

FORWARD
TAPE
MOTION

TAPE CHANNELS

CHARACTER

o
o
o

1
1
1

'-----------------------------------------------------------------------------------------~

LARSE~JRAtiA
IN BLOCK

-"r-f-----

r41--

EXTENDED IRG - - - -...
b. EOF

RECORD

EOF - + - I R G
RECORD
:3 BLANK
CHARACTER
PERIODS

-+
1

B~~IN:~~G

DATA BLOCK

11-0391

Figure 5-1 7-Channel Tape Format

The magnetic tape is divided into data records, each record separated by an interrecord gap (lRG). A record may
be any length from a minimum of 16 characters to a maximum of 4008 characters. In a block format, a number
of records are written together with an IRG before the first record and after the last record. In either case, the
IRG is an unused portion of tape preceding and following the record or the block.
The longitudinal parity check (LPC) character is written after the data and is separated from the data by three
character spaces. Each bit in the LPC is such that the total number of bits in any specific channel is even.

5-2

The end of a block of records is indicated by an end-of-file mark character. The end-of-file (EOF) mark is separated from the data by an extended IRG. The extended IRG is a 3-in. strip of blank tape compared to the standard 3/4-in. IRG for 7-channel tape and the 1/2-in. IRG for 9-channel tape. The EOF mark and associated LPC
character are considered to be one complete record.
The 9-channel tape format (see Figure 5-2) is similar to the 7-channel format; however, because each character
consists of eight data bits and one parity bit, a PDP-II byte corresponds to a tape character. Therefore, there is
no need for a core dump mode, because information can be transferred from the system to the tape on a one-toone ratio. In addition, the 9-channel format includes a cyclic redundancy check (CRC) character. Data is followed
by three character periods, the CRC character, three more blank character periods, and the LPC character. The
LPC character is followed by an IRG as before.

CHARACTER

,--_____-==~ ONE

89
7
6
5

l'
1
,
1

1
1
1

(PARITY)4

1
1

[-j-1

[~~i~~~J

BOT GAP

,1
1
1
1

,1
,
1
1

1
1 11
1 1
1 1
1 1

1
1
1

1W 1 1 ~ ~ 1 1

-t1

-,-

1
1
1

PDp·l' BYTE

CHA,-R_A_CT_E_R_ _ __

-CHDAA~:cTER-+CHAR~CTER+CHARhER t-INTE~~~CORD+ ~i~r
MIN,

PERIODS

(IRGl

RECORD
11-0392

Figure 5-2 9-Channel Tape Format

5.3 FUNCTIONAL DESCRIPTION
The prime function of the TM 11 Controller is to control transfers of information so that digital data can either be
taken from the bus and recorded on magnetic tape (write operation) or read from the magnetic tape and transferred to the bus for use by another device such as memory (read operation). In addition, the controller performs
tape transport selection, tape positioning, tape formatting, and system monitoring functions.
The controller contains a command regi'ster, which allows the program to specify desirec operations by loading
control data (transport selection, packing density, function, etc.) into the register. System status information
(end-of-tape, errors, tape unit ready, etc.) is loaded into a status register, which can be read from the bus.
The TMII Controller controls up to eight magnetic tape transports. Although any number of tape units may be
simultaneously rewinding, data transfers may take place with only one transport at any given time. The basic
functions performed by the controller are: off-line, read, write, write EOF, space forward, space reverse, writewith-extended-IRG, and rewind. Each of these functions is briefly described in Table 5-1.

5-3

Table 5-1
Controller Functions
Number

Function
Off-Line

Description
The off-line function is used when it is desired to return
control to the tape transport so that tape can be rewound,
reels changed, etc. without using processor time.
The off-line function places the selected tape transport in
the off-line (local) mode and causes it to begin a rewind
operation.
The TM 11 Controller cannot write on or read from the
magnetic tape when the off-line function is used.

Read

This function permits reading from the magnetic tape.
During the read operation, the data portion of the record
is loaded into the controller data buffer for transfer to the
memory. The LPC and CRC characters are read but not
transferred in to memory.

Write

This function permits writing on the magnetic tape. During
the write operation, data from the bus is loaded into the
controller data buffer register. The controller then transfers the data to the tape transport write heads. The
necessary LPC and CRe characters are generated by the
master transport and written on the tape following the
data. The write function advances the tape forward one
record.

Write EOF

This function writes an end-of-ftle (EOF) mark on the tape.
When selected, this function erases a 3-in. segment of tape
prior to writing the first character. The EOF mark and the
associated LPC character are considered one record.

Space Forward

This function is used to skip over a number of records to
find a specific record on the tape. When selected, the space
forward function causes the tape transport to advance
forward a specified number of records. The number of
records is determined by the value in the byte record
counter. This value is loaded into the byte record counter
by the program.
Space forward is used for tape positioning only and, therefore, does not affect information stored on the tape or in
memory.

Space Reverse

This function is identical to the space forward function except the tape moves in the reverse rather than in the
forward direction.

Write-with-Extended-IRG

This function is identical to the write function except that
a 3-in. segment of tape is erased before writing the first
character.

5-4

Table 5-1 (Cont)
Controller Functions
Function

Number
7

Rewind

Description
This function is used for rewinding the tape on the feed reel
so that the tape can either be unloaded from the transport
or operation can start at the beginning of the tape. When
this function is used, the tape moves in the reverse direction,
at a much higher speed (150 ips) than for other functions,
until the beginning-of-tape (BOT) marker is detected.
Rewind is used for tape positioning only and has no effect
on information stored on the tape or in the memory.

Data transfers are controlled by a byte record counter (MTBRC) and a current memory address register (MTCMA).
The program loads the byte rec.ord counter with the 2's complement of the desired number of data transfers.
The counter is incremented before each transfer; therefore. the byte transfer that causes the byte count overflow
(MTBRC becomes zero) is the last transfer to take place. The byte counter is also used to count the number of
records during space forward and space reverse operations.
The current memory address register is also incremented before each transfer and, therefore, always points to the
next higher address than the one most recently accessed. Thus, when the entire record is transferred, the register
contains the address plus 1 of the last character in the record. For certain error conditions, the register contains
the address of the location in which the failure occurred.
During read operations, the controller assembles bytes from successive characters read from the tape channels.
When reading a 7-channel tape, the six data bits are assembled in a data buffer register for temporary storage.
The parity bit is read but not loaded into memory. Because the PDP-ll uses 8-bit bytes, the remaining two bits
in the buffer are forced to O. When the byte is assembled, it is placed on the bus for transfer to memory. If an
NPR transfer is used, bytes from the data buffer are alternately stored into the low and high byte portions of
memory.
When reading 9-channel tape, operation is identical except that eight data bits are assembled. It is not necessary
to force any bits to 0, because the eight data bits constitute a complete PDP-II byte. In the case of both
7-channel an-d 9-channel tapes, the parity bit is loaded into the data buffer but is not loaded into memory.
When reading 9-channel tapes, either the CRC character of the LPC character at the end of a record is stored in
the data buffer, depending on the state of bit 14 in the MTRD. If this bit is 0, the CRC character is loaded into
the data buffer and can be used for error detection. If the bit is I, then the data buffer contains the LPC character
at the end of the record. When reading a 7-channel tape, bit 14 in the MTRD operates in a similar manner. If bit
14 is set, the LPC character is present, and when bit 14 is cleared, the last data character is present in the data
buffer.
During write operations, the controller disassembles 8-bit bytes from the bus and distributes the bits so that they
can be recorded on successive frames of the tape. The controller selects one of three recording densities (200,
556, or 800 bpi) for 7-channel tapes. All 9-channel tapes are written at a density of 800 bpi. There are three
possible write functions: write, write-with-extended-IRG, and write end-of-file (EOF) mark.
When a write function is selected, the program loads the byte record counter with the 2's complement of number of bytes to be written in the record. Although the parity bit, which is also loaded into the buffer, is generated by the TUI 0 Master Tape Transport, the polarity of the bit is determined by the controller so that either

5-5

odd binary or even BCD parity can be selected. When parity is generated and the buffer is loaded, the controller
transmits the byte to the master tape transport, which places the byte on the read/write heads of the selected
slave transport so that data can be written on the magnetic tape.
The write-with-extended-IRG function is identical to the write function except that a 3-in. gap, rather than the
normal gap is used between records. When this function is selected, a 3-in. segment of tape is erased before
writing begins.
The write end-of-file (EOF) function is used to indicate that a block of records is complete. When this function
is selected, a special EOF character is written on the tape followed by an LPC character. These two characters
constitute a complete record. This command causes a 3-in. gap to be placed before the EOF mark. The XIRG
command must be absent to have this gap written.
System monitoring functions are performed by the controller status register. The 16 bits in this register retain
error and tape status information. Some status data is combined, such as lateral and longitudinal parity errors, or
has a combined meaning, such as illegal command, for optimum use of the available bits. The status register only
monitors the tape transport selected by the command register; therefore, other units that may be rewinding, do
not interrupt the system when ready for data.
The following paragraphs discuss parity, gap shutdown, and function commands.

5.3.1 Parity
All parity characters are generated and read by the logic in the master tape transport rather than the controller.
However, a brief description of parity is included in this chapter, because an understanding of the parity function
is necessary for proper understanding of controller operation.
Whenever any command is issued that moves the tape forward, the master tape transport transmits an LPC strobe
(LPCS) pulse at the end of each record of a 7-channel tape or a CRC strobe (CRCS) pulse and LPCS at the end of
each record of a 9-channel tape.
During any write operation, the controller sends a write data ready (WDR) level to the master tape unit for each
character in the record to indicate that the controller is ready to transmit data to the transport. The master tape
transport then issues a write strobe (WRS) pulse that strobes the character from the controller data buffer register
into the tape unit for writing on the tape.
When the last WRS pulse causes the BYTE RECORD COUNTER register to overflow, the controller lowers the
WDR level and the master tape transport writes the CRC character (9-channel only) and then the LRC character
on the tape.
Whenever a slave tape transport is handling the magnetic tape being read or written, the control signals are still
generated by the master tape transport, and the necessary characters transferred from the master to the slave at
the appropriate time.
The parity bit tape character in 7-channel format and in 9-channel format can be written in even or odd parity. If
the master tape transport is writing even parity, then the parity bit is set or cleared so that the total number of
ones in the character is even. If odd parity is used, then the parity bit is set or cleared so that the total number of
ones in a character is odd. The type of parity to be used (odd or even) is determined by the PEVN bit in the controller command register.
A longitudinal parity check (LPC) is also performed on both tape formats. The master tape transport writes an
LPC character at the end of each data record. The bits in this character may be either 1s or Os. The character is
written in such a manner that the total number of bits in a channel (including the LPC character) is even.

5-6

In addition to lateral and longitudinal parity checks, the 9-channel tape format includes a cyclic redundancy check
(CRC), which checks the total number of data characters within a record or block. The lateral parity of the CRC
character is odd if the number of data characters within the block is even and is even if the number of data characters is odd.
The CRC character is generated by a 9-bit register in the master tape transport. All bits in a data character are exclusive ORed into this register, which shifts one position between each character transfer. If shifting causes a I in
the register bit corresponding to tape channel P, then the bits representing tape channels 2, 3,4, and 5 are inverted.
After the last data character is read, the register shifts a final time. At this point, al,1 bit positions except those
representing tape channels 2 and 4 are inverted. The register now contains the CRe character, which is written
on the tape.
The values described above are related to the physical location of the read/write heads as shown below.

Value ofCRC
Register Bit
Track No.

Most Significant Bit
O.¥ I
2
3
4

Least Significant Bit
7~

5.3.2 Gap Shutdown
The master tape transport employs a gap shutdown period to ensure a 3/4-in. blank gap of tape between records.

As soon as the master transport reads the LPC character, it times through the gap shutdown period and then sends
a stop command to the selected slave transport.
On receiving a stop command, the slave transport enters a settling down (SDWN) period, which is the time between
the stop command and the actual stopping of the tape. When the slave transport stops, it enters an idle period at
which time the tape unit ready (TUR) bit is set to indicate that the slave transport is now ready to accept a function command.
The master tape transport can accept and execute any new command during the settling period of the slave transport unless the new command is to the same slave transport and the new command causes the tape to move in a
different direction than before. In this case, the master transport does not accept the new command until the
slave transport has stopped, as indicated by a 0 in the SDWN bit and a 1 in the TUR bit (these two bits are part
of the controller'status register).
When a tape transport is given a stop command, a new command can be executed by another transport while the
first transport is coming to a stop.

5.3.3 Function Commands
The program selects the specific function to be performed by setting or clearing appropriate function bits in the
command register. When the program sets the GO bit in the command register, the operation defined by the
selected function occurs, and both the control unit ready (CU RDY) and tape unit ready (TUR) bits are cleared to
indicate that the controller and selected tape transport are currently engaged in an operation and cannot accept a
new command until the current operation is completed.
When the off-line function is selected, the tape unit goes off-line and then rewinds to the beginning-of-tape (BOT)
marker. As soon as the off-line command is given, both the CU RDY and TUR bits are cleared, thereby preventing
the controller and transport from accepting a new command. The master tape transport then clears the select remote (SELR) bit in the status register, indicating to the program that the slave transport is now off-line.

5-7

When a tape reverse operation (not rewind) is selected, the master tape transport enters the gap shutdown period
immediately after reading the first data character.
During a write function (write, write EOF, and write-with--extended-IRG), the CU RDY bit is set when the first
LPC character is read from the tape. For write EOF and write-with--extended-IRG functions, a 3-in. gap is erased
prior to writing the required data characters.
A write end-of-file (EOF) function causes a character to be written on the tape that indicates a block of data is
complete. This function writes an EOF character followed by an LPC character. These two characters constitute
one record. In an EOF record (see Figure 5-3), the EOF character and the LPC character are identical. Octal 17
is the EOF character for 7-channel tapes; octal 23 is the EOF character for 9-channel tapes.

OCTAL
LPC
17
(OCTAL 17)

CHANNELS

MOST SIGNIFICANT

LEAST SIGNIFICANT

OCTAL
LPC
23
(OCTAL 23)

CHANNELS

MOST SIGNIFICANT

(PARITY)

LEAST SIGNIFICANT
o.7-CHANNEL FORMAT

b.9-CHANNEL FORMAT
1/-0427

Figure 5-3 EOF Record

5.4 SYSTEM RELATIONSHIP
Figure 5-4 is a simplified block diagram of the TM 11 DECmagtape System, showing the relationship of the TM 11
Controller to the TUIO DECmagtape Transports and to PDP-II System components. Note that all communication between the controller and the transports is handled by the master tape transport. Communication between
the controller and other PDP-II devices is by means of the Unibus.
5.5 ADDRESS SELECTION
The TM II Controller selection logic decodes the address on the bus lines to determine if the controller has been
selected for use. Unique addresses are assigned to each of the six registers in the controller and manipulation of
these registers determines whether information is to be written on or read from the tape, or if some other control
function is to be performed.
The TMII Controller consists basically of six registers (or bus addresses). In addition to decoding the incoming
address, the selection logic controls the information flow between the Unibus and the controller registers. The
logic produces SELECT line and gating IN or OUT signals, which determine the register to be used and whether
it is to perform an input or output function.
The selection logic consists of an MI05 Address Selector Module and register select logic (M797 Module).

5-8

TO OTHER
DEVICES
ON BUS

MEMORY

COMMAND
TM11
CONTROLLER

DATA
STATUS

TU10
MASTER
TAPE
TRANSPORT

DATA

TU10
SLAVE
TAPE
TRANSPORT

DATA

TU10
SLAVE
TAPE
TRANSPORT

TO OTHER
DEVICES
ON BUS

UP TO
FIVE
ADDITIONAL
SLAVE
TRANSPORTS

11-0428

Figure 5-4 TM 11 System - Simplified Block Diagram

5.5 .1 Address Selector Module
The M 105 Address Selector Module (Drawing TM 11-0-21) decodes the address information from the bus to provide the gating and select line signals that activate appropriate TM II Controller logic circuits for the selected
register. The M I 05 Module jumpers are arranged so that the module responds only to the standard device register
addresses 772520 through 772532. Although these addresses have been selected by DEC as the standard assignments for the TMII Controller, the user may change the jumpers to any address desired. However, any MainDEC
program (or other software) that references the TM 11 standard address assignments must be modified if other
than the standard assignments are used.
A standard M 105 Module provides only four select line signals and, therefore, can reference only four registers.
Because the TM 11 Controller contains six registers, the M105 is used in conjunction with register select logic
(M797 Module) to provide the six required select lines. This necessitates wiring the M 105 in a somewhat different
than normal manner.
Rather than decode the entire incoming address, as is the normal method, the M 105 in the TMll Controller decodes all but the four least significant bits, These bits are then decoded by the register select module (M797
Module), provided the other bits are part of a valid address.
Address line AOO, which is the least significant bit of the address, is decoded by the M105 to determine if a byte
or word operation is required. Address lines AO 1, A02, and A03 are grounded and are the only address bits that
cannot be decoded by the M 105. Thus, the M I 05 decodes all but the four least significant bits of the incoming

5-9

address as shown in Figure 5-5. If the first portion of the address is valid (77252 or 77253), then the address
selector generates an ADRS DEC MSYN L (address decoded, master sync valid) signal that clears the decoders in
the register select logic (refer to Paragraph 5.5.2).

I
I DECODED BY REGISTER

DECODED BY THE MIOS.
BIT CONFIGURATION
SHOWN IS ONLY VALID
COMBINATION
7

SELECT LOGIC. MAY BE
ANY COMBINATION OF
Is AND Os

I
I
I

010

0 IIX

I
I

YYY

YIndicates value of final
digit. May be any value

(O-7).

Indicates whether next to
( last digit is 2 or 3.
Figure 5-5 M 105 Address Decoding

The MI 05 Address Selector also decodes the bus CO I and COO mode control signals to generate the IN, OUT LOW,
and OUT HIGH signals that determine whether the selected register is reading or writing (performing an input or
output function).
It is beyond the scope of this discussion to cover operation of the M I as Address Selector, detailed descriptions of

this module are covered in the 1971 DEC Logic Handbook and in the Unibus Interface Manual, Second Edition
(DEC-II-HIAB-D).
There are only two prime differences between normal use of the M I 05 and the use in the TM II Controller. Pin
L2 is normally a test point, but in the TM 11 it is used to provide the ADRS DEC MSYN L signal for the register
select. Address lines AD I, A02, and A03 are normally decoded by the M I 05, but in the TM II they are decoded
by the register select logic (M797 Module).

5.5.2 Register Select Logic
The gating signal lines from the M 105 Address Selector and address lines AO I, A02, and AD3 from the bus are
connected to the M797 Register Select Module (Drawing TM 11-0-22). This module decodes the address lines and
provides the pulses that select the appropriate register and determine whether the register is to be read or loaded.
The ADRS DEC MSYN L signal from the M 105 Module is applied to the register select module when valid addresses up to the least significant octal digit have been decoded. The ADRS DEC MSYN L signal gates the appropriate gating signal (IN, OUT La, OUT HI) to enable one of three decoders. If the M 105 has provided an IN
gating signal, then the first decoder (E2) is enabled, and one of the six outputs is selected by address lines AD 1,

AD2, and AD3. The IN gate indicates that data is beIng transferred into the bus master device, and the decoder
output selects the register from which the data is to be taken. Note that the decoder is actually enabled by the
absence of the two OUT signals rather than the presence of the IN signal (refer to Table 5-2).

5-10

Table 5-2
M797 Decoder Selection
Input Signal

Function Selected

Decoder Enabled

Remarks

Output Signals

IN(-OUTLO)
-OUT HI

Load

One for each register.

OUTLO

Load even byte

OUT HI

Load odd byte

Only four of the six registers can be loaded.

If the OUT La signal is supplied by the M I OS, the second decoder (E6) in the M797 Module is enabled, and the
address lines select one of five decoder outputs. The OUT signal indicates a load operation (data from bus to
master device). The first four outputs are used for the four registers that can be loaded from the bus. Note that
OUT LO loads only the low-order (even) byte in these registers. The fifth output is used to load bits 13 and 14
in the TUI 0 read lines.
If the OUT HI signal is received from the MI05, the third decoder (E9) is enabled, and the address lines select
one of four decoder outputs to load the high-order (odd} byte of the selected register.
Table 5-3 indicates the functions selected by the various select line and gating signal combinations.

Table 5-3
Gating and Select Line Signals
Select Line
Status
I

2
3
4

5
1

2
3
4

Gating Signal

Function

IN
IN
IN
IN
IN
IN

Status to bus
Command to bus
Byte record count to bus
Current memory address to bus
Data buffer to bus
TUI0 read lines to bus

OUT
OUT
OUT
OUT
OUT

Bus to command register
Bus to byte record counter
Bus to current memory address register
Bus to data buffer register
Bus to bits 13 and 14 of TU 10 read lines

•

Bus Cycle

MTS
MTC
MTBRC
MTCMA
MTD
MTRD

DATI or DATIP
DATI or DATIP
DATI or DATIP
DATI or DATIP
DATI or DATIP
DATI or DATIP

MTC
MTBRC
MTCMA
MTD
MTRD

DATa or DATOB
DATO or DATOB
DATa or DA TaB
DATO or DATOB
DATO or DATOB

NOTES: 1. IN and OUT refer to information transfer with relation to the bus master device.

2. Status register and TUI 0 read lines can be read by the processor but cannot be loaded by
the processor except for bit 14 of the TU I 0 read lines, which is the CRC/LPC character
selector bit, and bit 13 which is the BTE generator bit.
3. The OUT gating signal actually can be OUT LO or OUT HI. OUT LO loads the low-

order (even) byte; OUT HI loads the high-order (odd) byte.

4. The IN gating signal is actually (-OUT LO·""'OUT HI).

5-11

5.6 BUS CONTROL
The TMll Controller is interfaced to all other components of a PDP-II System by means of the Unibus. All control instructions and data transfers that take place between the TM 11 Controller and PDP-II components, such
as the processor and memory, must pass through this bus.
The bus control logic performs three main functions: NPR transfers, interrupts, and slave response. Each of
these functions is briefly explained in Table 5-4 and discussed in detail in the following paragraphs.
Table 5-4
Bus Control Functions
Function
NPR Transfer

Controller Status
Bus Master

Bus Cycle

Description

DATOB

The bus control logic requests control of the bus for
NPR data transfers whenever the controller is ready
to send data from the data buffer through the bus
to memory (read function). Transfers one byte at a
time.

DATI

The bus control logic requests control of the bus for
NPR data transfers whenever the controller is ready
to receive data from the memory (write function).
Transfers one byte at a time.

Interrupt Request

Bus Master

INTR

The bus control logic issues an interrupt request if
the controller requires servicing by the program,
because it is ready to transfer data, it is ready to
begin a new operation, it is awaiting a command, or
because an error condition exists. INT ENB in the
command register must be set.

Slave Response

Bus Slave

DATa
DATOB
DATI
DATIP

Whenever the TM 11 Controller is selected for use, it
must respond with SSYN in order for the command
instructions to be supplied by the processor or other
bus master. This logic provides the proper slave
response.

5.6.1 NPR Transfers
The NPR con trollogic circuits are shown on Drawing TM 11-0-21. The main portion of the control logic consists
of an M796 NPR Control Module. This module is used to control transfers of data to and from any slave device
on the bus when the controller is functioning as bus master. The transfers are performed independently of
processor control and are often referred to as "direct memory access".
The logic necessary to gain control of the bus is provided by the M7821 Interrupt Control Module (Drawing
TMII-0-21), which generates the non-processor request (NPR). When the proper responses are received from the
processor, the M7821 asserts BUS BBSY to indicate bus control. On becoming bus master, the controller is free
to conduct a data transfer. A DATI cycle is performed if the controller needs data from a bus address; a DATa
or DATOB cycle is performed if the controller transmits data to memory or some other device. Basically, a DATI
is used during write operations, a DATa or DATOB is used during read operations.

5-12

The bit that controls selection of a DATI or DATO is function bit 02 (Drawing TM 11-0-09). This bit is always
clear for a read operation (octal number 01) and is always set for write operations (octal numbers 02, 03, and 06).
Therefore, by using this bit for bus cycle selection, the proper cycle is used for the selected function (read=DATO,
write=DATI). The resultant read and write signals are applied to the NPR input logic (Drawing TM 11-0-13).
Whenever a read strobe (RDS) or write strobe (WRS) pulse from the master tape transport is sent to the controller
or whenever the WRITE DATA ENB and GO STROBE pulses are present in the controller, a series of gates is
qualified to produce a signal that sets the NPR enable flip-flop, provided there is no non-existent memory, bus
grant late, overflow error condition present, or no CRCS or LPCS strobe pulse present. This flip-flop produces
the NPR ENB H level, which initiates the NPR sequence.
The NPR ENB H level activates the Master Control A portion of the M7821 Interrupt Control Module (Drawing
TM 11-0-21), which generates a request on the BUS NPR line. When the processor has completed its current bus
cycle and all higher priority device requests have been satisfied, the processor issues a grant on BUS NPG IN. The
M7821 Module responds with BUS SACK and, when BUS SSYN, BUS BBSY, and BUS NPG are negated (indicating that the bus is free), the M7821 claims bus control by asserting BUS BBSY.
At this time, the M7821 Interrupt Control Module produces an NPR MASTER signal, which activates the M796
NPR Control Module (Drawing TM 11-0-21). This NPR MASTER signal produces an internal start signal in the
M796. Detailed descriptions of both the M7821 Interrupt Control and the M796 NPR Control Modules are provided in the Unibus Interface Manual, Second Edition, DEC-II-HIAB-D. Note, however, that in the Interface
Manual, the M796 is referred to as the Unibus Master Control Module.
Regardless of the bus cycle selected, a bus address must be used to indicate where the controller is to send or
receive data. The M796 Module produces the ADRS -+ BUS L signal, which enables the address line drivers in the
current memory address register (MTCMA) so that the data transfer is made with the location specified by the
MTCMA.
When a read operation is performed, the controller receives data read from the tape by the transport, assembles
the data in the data buffer register (MTC) and, when the data is properly assembled, sends the data to the bus.
This is a DATOB operation, because only one character is read from the tape at a time and the character corresponds to a PDP-II byte.
When a DATOB bus cycle is selected by the M796 Module, the module produces the DATA -+ BUS signal which,
together with a flip-flop and AND gates, produces al ternate HI DATA BYTE Land LO DATA BYTE L signals
(Drawing TM 11-0-17) that enable data buffer output gating logic (Drawing TM 11-0-16); thus, the information
stored in the data buffer register is gated onto the bus for storage in alternate memory byte locations. After the
necessary Unibus time delays, BUS MSYN is asserted and, thus, a slave device is selected. When the slave device
responds with SSYN, MSYN is dropped, and the bus cycle is complete.
When a write operation is to be performed, the controller receives the data from the Unibus, holds it temporarily
in the data buffer, and then transmits it through the read/write lines to the master tape transport electronics for

writing on the magnetic tape.
When a DATI is selected by the M796 Module, the module first produces the ADRS

BUS signal as usual but,

rather than produce a DATA -+ BUS signal, the M796 waits for the slave to respond and then produces two
sequential pulses: DATA STB 1 and DATA STB 2. The DATA STB 1 pulse allows time for the data on the
Unibus to deskew and settle. The pulse is also used internally (Drawing TM 11-0-22) to produce DATA BFR STB 1
and DATA BFR STB 2, which clear the data buffer register (MTD).

5-13

The trailing edge of DATA STB 2 is tied back into the M796 Module to produce an internal signal, indicating that
the data has been accepted. As a result of this signal, MSYN is dropped, and the bus cycle is complete.
On completion of either a DATI or DATOB bus cycle, the NPR CLR BBSY signal is generated. This signal is used
to increment the current memory address register (MTCMA). The NPR CLR BBSY signal also produces the
CLK 2 pulse (Drawing TM 11-0-07), which increments the byte record counter (MTBRC). The trailing edge of
NPR CLR BBSY direct clears the request bus flip-flop (Drawing TMII-O-13), which drops at the input to the
M7821 Interrupt Control which, in turn, drops BUS BBSY.
A time-out flip-flop, referred to as NXM (non-existent memory), in the M796 Module is set if a SSYN response
from the slave device does not occur within 10

j1S

after BUS MSYN is asserted by the controller. When this flip-

flop is set, the bus cycle is not performed, and the NXM error bit in the status register is set by the error logic circuits. In this case, the current memory address register is not incremented and, therefore, the register contains
the address of the erroneous location.

5.6.2 Interrupt Request
An interrupt request is generated when the controller is ready to send or receive data to or from the bus, or when-.
ever an error condition exists. Interrupt requests are controlled by the BR (bus request) input logic (Drawing
TMII-O-13) and by the M7821 Interrupt Control Module.
The BR interrupt flip-flop is used to generate the BR INT pulse, which activates the M7821 Interrupt Control.
Note that this flip-flop can be set only if the INT ENB bit is set.
When the ERR bit is set, it indicates that some type of error condition exists. In this case, the ERR pulse produces the SET CUR L pulse (Drawing TM 11-0-08), which sets the BR flip-flop.
When both the controller and tape transport are ready to perform a data transfer, an interrupt service routine is
used to perform the required bus cycle. In this case, the CU RDY signal and the TUR signal qualify an AND gate
that produces an output, which sets the BR flip-flop.

If a function command is issued but the GO bit remains cleared, INT ENB is set, and an interrupt initiated. If the
selected tape transport (as indicated by the SEL bits in the command register) completes the rewind operation
before a new command to that unit is received, then an interrupt is initiated. This logic is covered in Paragraph

5.9.
The M7821 Module provides the logic necessary to make bus requests and gain control of the bus (become bus
master). The module also includes the circuits necessary for generating an interrupt. The module contains two
completely independent request and grant acknowledge circuits (channels A and B) for establishing bus control.
The following paragraphs provide a brief description of both channels. A detailed description of the M7821
Module, including circuit schematics, is contained in the Unibus Interface Manual, Second Edition,
DEC-II-HIAB-D.
Channel A (master control A) is used only for NPR requests and is activated when the bus request flip-flop is set,
as described in Paragraph 5.6.1. The BR MASTER L signal from channel A activates the NPR control logic so
that an NPR DATI or DATOB bus cycle can be performed. No vector address is used with this channel.
Channel B (master control B) is used to generate interrupts (Drawing TM 11-0-24). This channel is activated by
the BR INT pulse described previously.

5-14

The jumpers on the M7821 Module are wired for a standard vector address of 224 and a bus request level of BR5.
Note that the priority level can be changed by the priority chip on the G736 Module, and the vector address can
be changed by jumpers on the M7821 Interrupt Control. However, any programs referring to that level or vector
address must also be changed if the jumpers are changed. All DEC software references the above standard jumpers.
5.6.3 Slave Response
When the TM 11 Controller is to participate in a data transfer as a bus slave device, the slave response logic provides
the necessary acknowledgement signals required by the bus master. This slave response logic is part of the M I 05
Address Selector and the M797 Register Select Modules.
For a DATO, the master device places the address of the TM II Controller on the hus A lines, data to be transferred
on the bus D lines, and signals on the bus C lines to select the appropriate register and function to be performed.
The master device waits 150 ns (75 ns to allow for worst case signal skew and 75 ns for address decoding) and then
asserts BUS MSYN, provided the bus is clear (SSYN is clear).
When the controller decodes the address, it produces the ADRS DEC MSYN L signal at the time MSYN is
received. The BUS MSYN L signal is gated through the MI05 to produce the BUS SSYN response. There is a
300-ns time delay between MSYN and generation of SSYN.
The master device receives SSYN, clears MSYN (which clears ADRS DEC MSYN L), Clearing ADRS DEC MSYN L
negates BUS SSYN to signify the end of the bus transaction.
5.7 BUS DRIVERS AND RECEIVERS
The bus drivers and receivers provide the signal levels required for compatibility with the Unibus. The M798
Transmitter Module contains bus drivers for interfacing controller outputs to the bus. The M784 Receiver
Module contains inverting circuits that provide buffered bus signal outputs, which are used as inputs to the controller. The M785 Transceiver Module contains both drivers and receivers that are used for bidirectional interfacing to the bus.
The bus receivers are used primarily on the input lines to the various controller registers; the bus transmitters are
used on the output lines. The transceivers are used on the current memory address register lines for bits 0 I, 02,
03, 16, and 17.
The M784, M785, and M798 Modules are described in the Unibus Interface Manual, Second Edition,
DEC-II-HIAB-D.
5.8 REGISTERS
All software control of the TM 11 Controller is performed by means of six device registers. These registers are
assigned Unibus addresses and can be read or loaded with any PDP-II instruction that refers to their address.
Note, however, that the status register and the TUIO read lines (with the exception of bits 13 and 14 in the read
lines) can be read but cannot be loaded from the bus. Bits 13 and 14 of the read lines can be loaded from the bus.
In addition, bit 13 is always read as a O. Table 5-5 lists the six registers and the function of each.
The register select logic provides the pulses that activate a specific register for use. This selection is described in
Paragraph 5.S.2.
Paragraph 5.8.1 describes the initialize (lNIT) logic, which is common to all registers. Subsequent paragraphs discuss each of the registers from a hardware standpoint. A discussion of the registers from a programming standpoint is presented in Chapter 4.

5-15

Table 5-5
Device Register Functions
Register

Mnemonic

Function

Status Register

MTS

Provides detailed information on the status of the TM 11
Controller. Such information includes error indications
and tape unit status indications.

Command Register

MTC

This is the main control register in the TM 11 Con troller.
Specifies the operation to be performed on the tape unit,
selects the tape bit packing density, and selects the tape
unit to be used.
Indicates when TM 11 Controller is ready, when an error
condition eXIsts, and when the controller is cleared.
Provides the two extended address bits for bus addresses.

Byte Record Counter

MTBRC

Counts the number of bytes in any write operation, the
number of records in a space forward or space reverse
operation, and the number of bytes in a read operation.
Desired byte count is preset by the program. When the
register counts the number of specified bytes, it prevents
further transfers.

Current Memory Address Register

MTCMA

Specifies the bus or memory address to or from which
data is transferred during read and write operations. After
each transfer is completed, the register is automatically
incremented by I (next byte location).
When BGL or NXM errors occur, the register contains the
address of the location in which the failure occurred.
Note that this register is incremented by 1 and, therefore,
accesses byte, rather than word, locations.

Data Buffer Register

MTD

Contains the information read from or written on the tape.
Serves as a buffer between the tape unit and the memory.

TUIO Read Lines

MTRD

Permits storage of data read from the tape transport. A
parity bit indicates the occurrence of a parity error and
the channel containing the error.
A character selector bit is used to select the last character
of a record that is to be loaded into the data buffer
register.
A timer bit is used for diagnostic purposes by measuring
the time duration of the tape operations.
A BTE bit is used to set CU RDY prematurely in order to
provide a bad tape error indication.

5.8.1 Initialize Logic
The TM 11 Controller logic can be initialized by one of the following methods:

5-16

Depressing the CLEAR switch on the maintenance panel.

Loading a 1 into bit 12 (POWER CLEAR) of the command register.

Issuing a programmed RESET Instruction.

Depressing the START switch on the PDP-II processor console.

Occurrence of a power fail by either the processor power supply or the controller power supply.

The controller initialization logic is shown on Drawing TM 11-0-19. When the maintenance panel CLEAR switch
is activated, it produces the MAN CLR L pulse, which passes through a series of gates to produce the INIT Hand
INIT L signals which clear all logic in the controller and in the master tape transport.
When a 1 is loaded into bit 12 of the command register, an AND gate is qualified by D 12 Hand SEL 1 OUT HIGH
H. When the AND gate is qualified, the INIT Hand INIT L signals are produced as before.
The remaining three methods of initialization (programmed RESET, processor START, power fail) all use external
logic to provide a BUS INIT signal input to the controller. This signal becomes INIT REC H and produces the
INIT Hand INIT L signals as before.
5.8.2 Command Register (MTC)

The command register is the main control register in the system and specifies the operation to be performed.
Each of the bits is discussed separately below, beginning with the most significant bit.
5.8.2.1 Error Bit (15) - The ERROR bit (bit 15) in the command register is the inclusive OR of all error conditions in the status register. Thus, if any error bit in the status register is set, it sets the ERROR bit in the com-

mand register. When any error condition occurs, it sets the appropriate flip-flop in the status register. The appropriate level from the flip-flop passes through a series of OR gates (Drawing TM 11-0-20) and sets the command
register error flip-flop, which produces the ERR H signal. The ERR H signal is then applied through a series of
AND gates (Drawing TM 11-0-15) so that the bit can be read from the bus.
Because of the gating shown on Drawing TM 11-0-20, the ERR flip-flop mayor Ill.ty not be set simultaneously
with the detection of an error condition. In the case of BGL (bus grant late), NXM (non-existent memory), ILC
(illegal command), and BTE (bad tape error) errors, the resultant error signal passes through OR gates and sets the
error flip-flop simultaneously with detection of the error.
If RLE (record length error), CRE (cyclical redundancy error), PAE (parity error), or EOF (end-of-file) occurs,
the appropriate status register flip-flop is set, and the resultant error signal is ANDed with the LRCSD signal,
which occurs only when the LPC character is detected. Thus, the command register error flip-flop is not set
until the LPC character has been read, in order to give the controller time to complete the current operation.
When the EOT (end-of-tape) marker is detected, it represents an error condition only if the tape is moving in the
forward direction. The EOT signal is ANDed with SPACE REV L, REWIND L, and LRSCD. This AND gate,
therefore, is qualified only if: the end-of-tape marker has been detected (EOT), the tape is not moving in the
reverse direction (SPACE REV L), the tape is not being rewound (REWIND L), and the LPC character has been
detected (LRCSD). If these conditions are met, the gate is qualified, and the resultant output sets the error
flip-flop in the command register.

5~17

When the ERROR bit is set, it sets the CU RDY bit (bit 07), as shown on Drawing TM 11-0-08. The ERR L
signal from the error flip-flop passes through 2 pulses and two OR gates to produce the SET CUR L signal that
direct sets the control unit ready (CU RDY) flip-flop.
The output of the interrupt flip-flop (BR INT H) is applied to the MASTER CONTROL B section of the M782l
Interrupt Control Module, and the TM 11 Controller initiates an interrupt routine. Thus, an error condition
causes an interrupt, provided the INT ENB bit is set.
A selection error is an illegal command and, therefore, also causes an error condition.
The error conditions can be cleared by INIT (refer to Paragraph 5.8.1) or by the next GO command.
5.8.2.2 Density Bits (14 and 13) - The DEN 8 and DEN 5 bits are used together to determine the bit packing
density of the tape. Densities of 200,556, and 800 bpi may be selected for the 7-channel tape, but only 800 bpi
can be used for the 9-channel tape. The program selects the density by loading the appropriate value into these
bit positions, according to the following table:
DEN 8
(Bit 14)

DEN 5
(Bit 13)

Selected bpi

200}
556
800

7-channel tape

800

9-channel

These values are applied to the master tape transport by the controller. The master tape transport contains the
actual density selection logic for the tape. The controller logic is used primarily to feed appropriate bits to the
master tape transport and to select the core dump mode of operation. Controller logic is shown on Drawing

TMII-O-I0.
When a I is loaded into bit 13 (DEN 5), it is applied to the D-input of a flip-flop. The clock input is the SEL I
OUT HI H signal that indicates the bus is loading the command register. These two inputs set the flip-flop.
The low side of the flip-flop qualifies an AND gate, provided the core dump mode is not being used. The output
of the AND gate is the DEN 5 signal (representing binary I) that is applied through the BC 1 1A interconnecting
cable to master tape transport.

If a 0 is loaded into this bit position, the flip-flop is not set, the AND gate is disqualified, and the AND gate output is a low level representing binary O.
The DEN 8 (bit 14) signal is produced in an identical manner to the DEN 5 signal.
The core dump mode is used with 7-channel tapes when it is desired to use all bits within a memory byte. Normally, the two most significant bits in a byte are not used. During core dump mode, all bits are used, but the
two most significant channels on the tape are not used. In effect, two tape characters are used to represent one
byte as shown in Table 5-6.
The core dump mode is enabled whenever the program sets both DEN 5 and DEN 8 to a I while the 7-channel
(7CH) signal from the master tape transport is a I, indicating that a 7-channel tape is being used. When both the
DEN 5 and DEN 8 flip-flops are set, the DEN 5 H and DEN 8 H signals are applied to an AND gate that is qualified by the 7CH H signal from the master transport. A signal produced from this AND gate is CORE DUMP H,
which disqualifies the AND gate from the low side of the DEN 5 flip-flop so that the DEN 5 signal to the master

5-18

transport is a O. This is necessary because both DEN signals had been 1s in order to select the core dump mode,
but a 10 code must be applied to the master transport in order for the actual transfer to take place at 800 bpi.
The core dump mode is used for reading and writing on tape. It is important to note that the TU 10 tape channels
are numbered in the reverse order of the data buffer bits. Thus, for example, data buffer bits 0, 1, 2, and 3 correspond to tape channels 7,6,5, and 4, respectively.
After the core dump mode has been properly selected, the resultant CORE DUMP Land 7CH L pulses disqualify
the four AND gates connected to tape channels 3, 2, I, and 0 (Drawing TM 11-0-11). Channels 1 and 0 are disqualified by 7CH, because they are used only during 9-channel operation; tape channels 3 and 2 are disqualified
by CORE DUMP L, because they are not used during the core dump mode of operation.
When transferring data from the data buffer register to the master tape transport during the core dump mode, one
8-bit PDP-II byte is written as two 4-bit tape characters. This is accomplished by the gating shown on Drawing
TM 11-0-11 and is in the form shown in Table 5-6.

Table S-6
Core Dump Mode
First Tape Character

Second Tape Character

4
5

Corresponding TU 10 Write Lines
WD7
WD6
WD5
WD4

NOTE: These two characters represent one byte with 0-7 bits.

5.8.2.3 Power Clear Bit (12) - When the program loads a 1 into this bit position, an initialize signal is provided
to clear the TMll Controller, the master tape transport, and the slave transports. This initialize signal does not
clear the processor or any other device on the bus. The initialize signal is generated by the controller logic as
described in Paragraph 5.8.1. The INIT signal passes through a gate and becomes the CINIT signal, which is
applied to the master tape transport logic to clear all transports.
5.8.2.4 Parity Bit (11) - The parity bit (bit 11) specifies whether odd or even lateral parity is to be read from or
written on the magnetic tape. Although parity is generated by the master tape transport, the parity bit in the controller command register is used to select the polarity. The parity bit is referred to as the PEVN (parity even) bit,
because it denotes even parity when set.

The parity flip-flop is shown on Drawing TM 11-0-1 O. The flip-flop is set by SEL lOUT HI H (indicating that the
command register has been selected for loading from the bus) and by D 11 H (indicating that a 1 has been loaded
into bit 11 of the command register). With the flip-flop set, the low side passes through a gate and becomes the
PEVN signal, which is applied to the master tape unit to indicate that even parity is to be used.
The parity flip-flop is cleared by loading a 0 into bit 11 (the D 11 H input becomes low) or by an INIT signal,
which direct clears the flip-flop. When the flip-flop is clear, the resultant PEVN signal is low, indicating to the
master tape transport that odd parity is to be used.

5-19

5.8.2.5 Unit Select Bits (10, 09, 08) - The three unit select bits (bits 10 through 08) specify the tape transport
that is to be used for a particular operation. The states of these three bits represent an octal code corresponding
to the number of the transport, as set by the UNIT SELECT switch on the individual transport.
The three unit select bits are shown on Drawing TM 11-0-12. These three bits (UNIT SEL BIT 2, UNIT SEL BIT 1,
and UNIT SEL BIT 0) are set or cleared by loading Is or Os from bus lines 10,09, and 08, respectively. The
UNIT SEL BIT signals are applied to one side of a flip-flop. The other side of the flip-flop receives the
CLK UNIT SEL L signal. Therefore, these flip-flops are set or cleared, depending on the UNIT SEL BIT signal.
This results in SEL 2, SEL 1, and SEl 0 signals (representing the appropriate octal code loaded from the bus),
which are applied to the master tape transport logic. The ClK UNIT SEl 1 signal is produced, provided the
following conditions exist: the command register is being loadtrl from the bus (SEllOUT l), the master tape
transport is off-line (SEL R), is rewinding, or is not in either the tape operation time (CU RDY is 0) or gap shutdown time.
The three SEL signals are applied to a binary-to-octal decoder within the master tape transport. Depending on
which signals are high, one of the eight tape units is selected for use.
It is possible that the desired tape unit may not be properly selected. For example, there may be no tape trans-

port UNIT SELECT switch that is set to the number loaded by the program. Another instance of improper
selection would be selecting a tape transport that is off-line. In either case, improper selection is an illegal command (lLC) error, which, in turn, causes an ERR indication.
The unit select logic also produces UNIT SEL BIT TM Hand 1 signals, which are used by the tape motion control
logic described in Paragraph 5.9.
5.8.2.6 Control Unit Ready Bit (07) - The control unit ready bit (bit 07) indicates that the controller is ready to
receive a new command. It is set (indicating ready) whenever the previous command operation is completed, an
initialize" signal is given, or an error condition exists. It is cleared at the beginning of a tape operation when the
GO command (bit 00) is issued.
The control unit ready flip-flop is shown on Drawing TM 11-0-08. A series of gates is connected to the direct-set
input of the flip-flop. If the INIT signal goes high (indicating initialize) or the ERR signal is presen t (indicating
some type of error condition exists), the output of the OR gate goes low and direct sets the control unit ready
flip-flop, producing CU RDY H.
The gating also direct sets the CU RDY bit when: the byte record counter overflows with space forward or space
reverse operations; when the first LPC character is read in a tape forward command which is not a SPACE
FORWARD; when a rewind operation has started; when the unit goes off-line during an operation; and when the
BOT is sensed during a rewind or SPACE REV operation.
The control unit ready flip-flop is cleared by the GO BIT H signal, which occurs whenever the GO bit is loaded
from the bus.
5.8.2.7 Interrupt Enable Bit (06) - The interrupt enable (lNT ENB) bit, when set, allows an interrupt to occur
provided either CU RDY (bit 07) or ERR (bit 15) becomes set. It also permits an interrupt whenever a tape unit
in the rewind mode reaches the BOT marker at the time CU RDY is a I, or whenever an instruction sets the
INT ENB bit but does not set the GO bit (Bit 00).

5-20

The interrupt enable flip-flop is shown on Drawing TM 11-0-1 O. It is set by SEL lOUT LO H (bus loading
command register) and D06 H (a 1 in the bit position). The high output of the flip-flop (lNT ENB H) qualifies
one side of an AND gate, tied to the input of the bus request flip-flop (Drawing TM 11-0-13). The other input
to the AND gate is produced by a series of gates corresponding to the conditions mentioned above. Thus, when
the ERR bit is set (indicated by SET BR L pulse); or when a tape unit has completed its rewind operation (indicated by RWS H and BOT H); or when an instruction sets the INT ENB bit but does not set the GO bit (indicated by INT ENB L, DOO L, and SEL lOUT LO H), the AND gate is qualified, thereby setting the BR INT flipflop.
The INT ENB bit is direct cleared by the INIT L signal or is cleared by loading with a 0 (input D06 H becomes
low).
5.8.2.8 Extended Bus Address Bits (OS and 04) - The extended bus address bits 05 and 04 represent bus address
bits A 17 and A 16, respectively. These bits are used to specify I8-bit addresses when required, because the current
memory address register (MTCMA) is only 16 bits long. Although functionally part of the MTCMA, these bits
are loaded by a SEL 1 OUT LO H signal, which indicates that the command register has been selected for use.
The current memory address register is incremented after each data transfer, and this incrementation also affects
the two extended address bits. These bits are cleared by INIT, as shown on Drawing TM 11-0-22.
5.8.2.9 Function Bits (03, 02, 01) - The three function bits are set or cleared to provide an octal code that
selects anyone of eight commands that control operation of the tape system. These commands are used for
reading data from or writing data on the tape and for controlling tape motion.
The three function bits are shown on Drawing TMII-0-09. The appropriate 1 or 0 on the associated bus data
line (D03, D02, and DO 1) is loaded into the associated function flip-flop by means of a load pulse, which is
SEL lOUT LO H (command register selected for loading from the bus).
The FUNCTION BIT H line from each of the three flip-flops is tied to the input of an M 163 Binary-to-Octal
decoder, which decodes the state of the three bits and provides the selected function output signal. The selected
function signal is then applied to other controller logic to institute the function. Other logic that uses the function signals include: ready control logic, motion control logic, start control logic, error logic, and tape interface
logic.
5.8.2.10 Go Bit (00) - The GO bit is set by loading with a 1 from the bus and is used to initiate operation of
the function selected by the function bits.
The GO flip-flop (TM 11-0-06) is set by the SEL 1 OUT LO L signal (command register selected to receive data
from bus) and the DOO H signal (1 loaded into bus data line 00). Note that the output of the flip-flop, when set,
passes through a series of gates to produce three derivatives of the GO signal. These derivatives (shown in
Figure 5-6) are: GO STROBE 1, GO STROBE 2, and SET. The SET signal is effectively the GO pulse to the
master tape transport and must be present before any tape operation can be initiated.
The GO flip-flop is cleared by INIT or cleared by the GO STROBE 2 pulse. GO STROBE 2 is simultaneously
applied to an OR gate, the output of which direct cJears the GO flip-flop, and to an AND gate which, when
qualified, asserts the SET pulse (Go command to transport).
During normal operation, the GO pulse is 1 J..LS in duration. However, in some instances this duration may be
considerably longer, depending on the status of the selected tape transport.

5-21

GO STROBE 1

GO STROBE 2

SET
NOTES:
1. All signals are lps in duration
2. Go signal is normally 1ps but may be 10ms or longer depending on what time
the bit is set (see text)
//-0429

Figure 5-6 Derivatives of GO Signal

As mentioned previously, the GO pulse cannot go low until the GO STROBE 2 pulse is generated. Before
GO STROBE 2 can be generated, a 4-input AND gate must be qualified. The four conditions needed to qualify
this AND gate are: GO BIT H (GO flip-flop is set), GSD L (Transport not in gap shutdown period), unit has
completed a rewind instruction, and the logic has determined that a GO can be sent to the transport during the
SDWN time. If anyone of these four conditions is not true, the GO pulse remains high until the required condition becomes true.
If the transport is in a gap shutdown or settling down period, the GO bit duration could be as long as 10 ms, depending on what point in the period the GO bit was set. If the selected tape unit is not ready (note that this
condition also exists during rewind, because RWS direct sets the flip-flop, providing one of the AND gate inputs),
the GO bit duration could be as long as several minutes as would be the case when the selected tape unit is in
the process of rewinding.
The GO BIT H signal is also applied to the control unit ready (CO RDY) flip-flop (Drawing TMII-O-08) to clear
the CU RDY bit. This is necessary because whenever the GO bit is present, it indicates the controller is performing an operation and is not ready to accept a new command.
5.8.3 Status Register (MTS)
The status register is used primarily to provide indications of error conditions. It also indicates the status of certain system functions such as write lock, settling down period, tape unit ready, and beginning of tape.
The status register error logic is shown on Drawing TMII-O-20. Whenever one of the specific error signals is
present, it passes through an OR gate, which is the inclusive OR of all error conditions. The resultant flip-flop
output signal (ERR L) passes through a pulser and two OR gates in the ready control logic (Drawing TMII-O-08)
and direct sets the control unit ready (CU ROY) flip-flop. This allows the controller to issue an interrupt request whenever an error exists (refer to Paragraph 5.6.2).
All error bits (15 through 06) in the status register are read-only bits. They can be read (tested) by the program
to determine if a specific error exists or not, but they cannot be loaded by the program. All error bits are cleared
by INIT or by the GO (GO STROBE 1) pulse to the tape unit.

5-22

The remaining bits (05 through 00) indicate system status and are set or cleared by the master tape transport.
These bits can also be read by the program.
Each individual bit in the status register is discussed separately in the following paragraphs.

5.8.3.1 Illegal Command (15) - The illegal command (ILC) error is bit 15 of the st~tus register and indicates a
conflict in commands. The ILC error logic (Drawing TM 11-0-19) consists of a series of gates and a flip-flop.
The first series of gates is used to direct set the ILC flip-flop. Any time that a DATO or DATOB transfer is made
to the command register (SEL lOUT LO H or SEL lOUT HI H) during a current tape operation (CUR DEL L),
gating is qualified to set the ILC flip-flop, because the command register cannot accept a new command while in
the process of executing another command.
When the SELR bit becomes 0 (SELR H) during any operation (CUR DEL L) except an off line command, gating
is qualified to direct set the ILC flip-flop, because no command can be issued to a tape transport that is not online.
The remaining gates in the ILC error logic are used to produce SET ILC H, which sets the ILC flip-flop when the
GO pulse is present (GO STROBE 2 L). There are two illegal commands that can produce SET ILC H.
The first command is any command to a tape transport that has its SELR bit clear (SELR H), because when
SELR is clear it indicates the transport is off-line.
The second illegal command is any write, write end-of-file, or write-with-extended-IRG command (WRITE ENB H)
that is issued when the write lock bit is set (WRL H), Writing is inhibited with WRL set, and all write commands
are, therefore, illegal.
When an illegal command produces the ILC H pulse, the pulse is applied to the gating logic for the error flip-flop
in the command register (Drawing TM 11-0-20); thus, the command register ERR bit is set simultaneously with the
status register ILC bit.
The ILC error bit is cleared by INIT or by occurrence of the GO pulse. When the GO pulse occurs, the GO
STROBE I pulse occurs immediately preceding the GO STROBE 2 pulse and is used to direct clear the ILC flipflop.

5.8.3.2 End-of-File Bit (14) - Bit 14 in the status register is the end-of-file (EOF) bit that is used to indicate
that the tape has reached the end of the file. The EOF flip-flop (Drawing TM 11-0-20) is set by the master tape
transport and cleared by INIT or GO pulse. The input to the flip-flop is the FMK (file mark) signal from the
master tape transport. This signal, when present, indicates that the transport has detected the end-of-file mark
on the tape. The signal sets the EOF flip-flop to produce the EOFF H signal.
It is beyond the scope of this manual to describe the logic used by the master tape transport to detect the end-of-

file mark. The transport logic is covered in the TV 10 DECmagtape Manual. A brief description of the EOF bit is
presented in Figure 4-1 of this manual.

5.8.3.3 Cyclic Redundancy Error Bit (13) - The cyclic redundancy error (eRE) bit in the status register indicates that the cyclic redundancy check for a 9-channel tape has detected a parity error. This check compares the
CRC character written during a write or write-with-extended-IRG operation with the CRC character generated
during a read operation.
The comparison of the two CRC characters is performed by logic within the master tape transport. If the two
characters are not identical, then the CRCE from the tape unit becomes a 1 and is applied to gating logic in the
controller error circuits (Drawing TMII-0-20). The gating logic sets the CRE flip-flop to produce CRE H.
5-23

The CRE output of the flip-flop is applied to gating logic associated with the command register ERR flip-flop.
Note, however, that the AND gate is not qualified until both CRE and LRCSD H are present. The latter signal
indicates that the LPC character has been detected. Thus, when a CRC error is detected, the CRE bit in the
status register is set immediately, but the ERR bit in the command register is not set until the LPC is detected.
This gives the controller time to complete the current operation before branching to an error routine by means
of the interrupt.
5.8.3.4 Parity Error Bit (12) - The parity error (PAE) bit in the status register indicates that a parity error exis(s
in the data. The error may be in either lateral (vertical) or longitudinal parity. A lateral parity error is indicated
for any character in a record; a longitudinal parity error indicates an error in a specific channel.
The parity error circuits are shown on Drawing TMII-0-20. An AND gate output is used to set the PAE flip-flop;
this AND gate is qualified by three inputs. The first input is RDS H from the master tape transport, which is used
to sample parity. The second input is either WRITE ENB or READ, because parity is checked during both read
and write operations. The third input is either the VPE (vertical parity error) or LRCE (longitudinal parity error)
signal from the transport. Thus, both lateral (vertical) and longitudinally parity errors are detected during read,
write, write EOF, and write-with-extended-IRG operations. The entire record is checked, including the CRC and
LPC characters.
Note that longitudinal parity occurs when an odd number of I s is present in any channel in the record; lateral
parity errors may be even or odd, depending on the setting of the PEVN bit in the command register.
The PAE output of the parity error flip-flop is applied to command register gating logic in the same manner as the
CRE output, as explained previously. In the case of PAE, the PAE bit in the status register is set immediately,
but the command register ERR flip-flop is not set until detection of the LPC character.
5.8.3.5 Bus Grant Late Error Bit (11) - The bus grant late (BGL) error flip-flop is bit II of the status register.
During normal operation, the controller makes an NPR request to gain control of the bus and initiate a data
transfer (either a read or a write). If the controller is still engaged in the NPR transfer when another NPR request
is initiated, a BGL error condition occurs.
The BGL flip-flop is shown on Drawing TM 11-0-20. It is set (indicating an error) when both the NPR ENB and
NPR SET inputs are high. These inputs are received from the NPR input logic (Drawing TMII-O-13).
If the controller receives either a WRS or RDS pulse from the master tape transport, the NPR logic circuits produce the NPR SET H pulse. This pulse is gated through an AND gate and sets the NPR request flip-flop on its

trailing edge.
If, however, the NPR transfer is still occurring when the next NPR SET H pulse occurs, the BGL flip-flop is set

to indicate an error. The NPR request flip-flop is cleared at the end of an NPR transaction by the
NPR CLEAR BBSY H signal.
The BGL error signal disqualifies the AND gate on the input of the NPR request flip-flop, thereby preventing any
further NPR requests until the error condition is corrected. In addition, the BGL signal is applied through gates
in the error logic (Drawing TMI 1-0-20) to set the ERR flip-flop in the command register.
5.8.3.6 End-of-Tape Bit (10) - The end-of-tape (EOT) bit is bit 10 in the status register. This bit is set when
the EOT marker is detected when the tape is moving in the forward direction; it is cleared by the trailing edge of
the EOT marker when the tape is moving in the reverse direction. Note that the EOT bit is an error condition
only when the tape is moving forward.

5-24

The EOT bit is controlled by the master tape transport. The transport logic detects the EOT and sends the
appropriate signal to the status register to set or clear the bit. When the EOT marker is detected by the transport,
the EOT H signal is applied to error logic in the controller (Drawing TMll-0-20). An AND gate is qualified if
EOT is high, and both SPACE REV L and REWIND L are true (indicating the tape is not moving in the reverse
direction). The output of the AND gate is ANDed with the LRCSD H signal (indicating that the LPC character
has been detected) and used to set the ERR flip-flop in the command register.
Thus, the EOT bit in the status register is set or cleared as soon as the EOT marker is detected, but the ERR bit
in the command register is not set until the LPC character has been read in order to allow completion of the current operation prior to initiating an interrupt.

5.8.3.7 Record Length Error Bit (09) - During read operations, the record length error (RLE) bit is set if the
master tape transport attempts to load another character into the controller after the number of bytes specified
by the byte record counter has already been transferred to memory. This error bit is used for long records only
and is set as soon as the byte record counter increments beyond O.
The byte record counter (MTBRC) is used to keep track of the number of data bytes loaded into memory from a
tape record. Initially, the MTBRC is loaded with the 2's complement of the number of bytes to be loaded. Each
time the master tape transport reads a character, it loads it into the data buffer register. After a byte is transferred
to memory, the MTBRC is incremented by 1. When the last byte is transferred to memory, incrementing the
MTBRC by I sets it to O.
As soon as the byte record counter goes to 0, it produces a CARRY OUT 2 L signal, which sets the OVERFLOW
flip-flop (Drawing TM 11-0-20). This flip-flop had been reset because of the INIT
is now set and produces an OVERFLOW H pulse.

GO L signal. Therefore, it

This overflow pulse is applied to one leg of a 3-input AND gate. Because the RLE error can only occur during a
read operation, the AND gate is not qualified unless a read operation is being performed as indicated by a read
strobe signal (READ STB H) and the absence of a CRCS or LRCS pulse (CRCS L or LRCS L). When the AND
gate is qualified, its output changes the state of the RLE flip-flop, thereby setting it to provide an indication of
record length error in status register bit position 09.
When the RLE flip-flop is set, the RLE L output qualifies an OR gate in the error logic circuits. The signal from
the OR gate qualifies an AND gate when the LPC character is read (LRCSD H), thereby setting the ERR flip-flop.
Thus, when a record length error occurs, the RLE bit is immediately set, and the ERR bit in the command register is set after the current operation is completed.

5.8.3.8 Bad Tape Error Bit (08) - A bad tape error occurs when a character is detected (RDS pulse) during the
gap shutdown or settling down period for all tape functions except rewind and off line.
The bad tape error flip-flop (Drawing TM 11-0-19) is normally in the clear state. It is set by the output of a
4-input NAND gate. One input of this NAND gate is the RDS H pulse, which indicates that a character has been
detected. The second input to the NAND gate comes from a series of gates that are qualified if the tape unit is in
either the gap shutdown (GSD L) or settling down (SDWN L) period. The third input is in the INH BTE signal
(BGL, NXM, or ILC is true). Issuing a new GO command or an INIT pulse causes the bad tape error flip-flop to
clear so that it can be ready for another bad tape error.
When the bad tape error flip-flop is set, it also qualifies one leg of an OR gate shown on Drawing TMII-0-20.
The output of this gate sets the ERR flip-flop as soon as the error occurs.

5-25

5.8.3.9 Non-Existent Memory Bit (07) - The non-existent memory (NXM) error flip-flop is bit 07 of the status
register. When set, this bit indicates that the controller was bus master during NPR operations but did not receive
a SSYN response from the slave device within 10 I1S after the controller issued the MSYN signal. The ERR bit is
set simultaneously with the NXM bit, thus terminating all operation. If the NXM error occurs during a write or
write-with-extended-IRG operation, the controller does not send the WDR signal to the master tape transport;
however, the master transport writes the eRe character (if required) and the LPe character onto the tape.
The NXM error flip-flop is part of the NPR control circuits on the M796 Module and is described in Paragraph
5.6.1.
5.8.3.10 Select Remote Bit (06) - The select remote (SELR) bit is bit 06 of the status register and, when set,
indicates that the selected transport has been selected and is on-line. When this bit is 0, it indicates that the tape
transport addressed does not exist (no transport UNIT SELECT switch set to the number specified by the program), is off-line (transport ON-LINEjOFF-LINE switch set to OFF-LINE), or that the selected transport has its
power turned off.
The select remote logic is within the master tape transport, which supplies the appropriate signal to the status
register for monitoring.

5.8.3.11 Beginning-of-Tape Bit (05) - The beginning-of-tape (BOT) bit in the status register indicates when the
BOT marker on the magnetic tape is read. As long as this bit remains 0, it indicates that the BOT marker has not
been sensed. When the bit is aI, it indicates that the marker has been sensed, and the beginning of the tape has
been reached. The ERR bit is not set when the BOT bit is sensed, because sensing of the BOT marker does not
indicate an error condition.
The beginr:ing-of-tape logic is within the master tape transport, which supplies the appropriate signal to the status
register to set or clear the BOT bit.

5.8.3.12 7~hannel Bit (04) - This bit is set or cleared by the master tape transport to indicate whether a
7-channel or 9-channel tape is being used. When the bit is set, it indicates a 7-channel tape; when it is clear, it
indicates a 9-channel tape.
The 7-channel bit is also used in conjunction with the DEN 8 and DEN 5 bits in the command register to cause
the core dump mode of operation. When these three bits are all set, the core dump mode is used, and all bits
within each byte in a memory location are transferred to the tape. A detailed discussion of the core dump mode
is presented in Paragraph 5.8.2.2.

5.8.3.13 Settle Down Bit (03) - A settling down period is provided to allow the tape to fully deskew prior to
stopping or starting a new operation. This settling down period sets the SDWN bit in the status register. When the
tape unit stops, SDWN is cleared, and the tape unit ready bit is set.
The settle down logic is within the master tape transport, which supplies the appropriate signal to set or clear the
SDWN bit in the status register. A description of the SDWN bit is contained in Paragraph 4-2 of this manual.

5.8.3.14 Write Lock Bit (02) - The write lock (WRL) bit is under control of the master tape transport. When
set, it prevents the controller from writing information on the magnetic tape. If the write lock signal is supplied
from the master tape transport (WRL H) and the controller attempts to write on the tape (WRITE ENB H), then
an AND gate is qualified (Drawing TM 11-0-19) that sets the illegal command (ILe) flip-flop, thereby setting the
ERR flip-flop and preventing the write operation from being executed.

5-26

5.8.3.15 Rewind Status Bit (01) - The rewind status (RWS) bit is under control of the master tape transport,
which supplies the signal to set or clear the RWS bit in the status register. The RWS bit is set at the start of a rewind operation, and becomes a 0 as soon as the BOT marker is detected while the tape is moving in the forward
direction. Thus, when the bit is set, it indicates the tape is rewinding; when it is clear, it indicates the rewind
operation is complete. The RWS signal from the master tape transport is also used in the tape control ready logic
described in Paragraph 5.9.3.
5.8.3.16 Tape Unit Ready Bit (00) - The tape unit ready (TUR) bit is under control of the master tape unit,
which supplies the signal to set or clear the TUR bit in the status register. Whenever the selected tape unit is being
used (such as rewind), this bit is cleared. When the tape unit is stopped and ready to receive a new command, this
bit is set. The TUR signal from the master tape transport is used in the tape start control logic described in
Paragraph 5.9.4.

5.8.4 Byte Record Counter (MTBRC)
The byte record counter (MTBRC) is a 16-bit binary counter used to count bytes in a read or write operation and
used to count records in space forward and space reverse operations. This register and the current memory address register constitute the M795 Module shown on Drawing TM 11-0-21. A detailed schematic and associated
description of this module is presented in the Unibus Interface Manual, Second Edition, DEC-l1-HIAB-D.
When used in a write or write-with-extended-IRG operation, the register is set by the program to the 2's complement of the number of bytes to be written on the tape. Each time a write operation is performed, the register increments by 1. After the last byte has been strobed from memory, the register increments to 0 and produces a
CARRY OUT 2 signal. This signal sets the OVERFLOW flip-flop (Drawing TMI1-0-20), which produces the
OVERFLOW signal. When the next write strobe (WRS) signal occurs, the OVERFLOW signal clears the write
data ready (WDR) line (Drawing TMII-0-09); thus, the controller lowers the write data ready line to indicate
to the master tape transport that there are no more data characters in the record.
When used in a read operation, the byte record counter is set to a number equal to or greater than the 2's complement of the number of tape characters to be loaded into memory. A record length error (RLE), which occurs for
long records only, occurs whenever a read pulse is generated after the MTBRC is at O. The RLE error is shown on
Drawing TMl1-0-20. The RLE flip-flop is set by the output of an AND gate that is qualified if the MTBRC has
incremented to 0 (OVERFLOW H), a read pulse is generated (READ STB H), and there is no CRCS or LRCS
pulse (""CRCS + LRCS).
When the MTBRC is used in a space forward or space reverse operation, it is set to the 2's complement of the
number of records to be spaced. The counter is incremented by I at LPC time, regardless of direction of tape
motion. A new GO pulse is sent to the tape unit during the SDWN time if the MTBRC is not yet at O. This logic
is shown on Drawing TMII-O-06. Either direction (SPACE FWD or SPACE REV) qualifies an OR gate to produce
SPACE H, which is one leg of an AND gate. The other leg of the gate is qualified if the MTBRC is not at 0
(OVERFLOW L), and there is no end-of-file mark (EOF F L). The output of this AND gate qualifies another
AND gate, provided settle down is present (SDWN H). When this gate is qualified, it triggers the logic that produces the GO pulse.
When the last record is reached, the byte record counter increments to 0 and produces the CARRY OUT 2 pulse.
This pulse is ANDed with SPACE H (Drawing TMII-O-08), passes through two OR gates, and direct sets the
CU RDY flip-flop. When this flip-flop is set, it indicates that the controller is ready to receive a new command,
because the space operation is now complete.

5-27

5.8.5 Current Memory Address Register (MTCMA)
The current memory address register specifies the bus or memory address to or from which data is to be transferred during write or read operations. The current memory address register (MTCMA) and the byte record counter
(MTBRC) constitute the M795 Module shown on Drawing TM 11-0-21. A detailed schematic and associated
description of this module is presented in the Unibus Interface Manual, Second Edition, DEC-II-HIAB-D.
Before issuing a command, the program loads the MTCMA with the memory address that is to receive the first
byte of data (read operation) or the memory address from which the first byte is to be taken (write operation).
After each memory access (read or write), the MTCMA is immediately incremented by 1. This incrementation is
caused by the NPR CLR BBSY signal, which indicates the bus transfer is completed.
The logic shown on Drawing TMII-O-22 is used to carry the bus address register incrementation to extended address bits 16 and 17 in the status register. When increment~tion of the MTCMA causes the register to contain all
Is, the next clock pulse sets the current memory address register to all Os and produces a CARRY OUT 3 pulse,
which sets extended address bit 16. The MTCMA then continues incrementing until another CARRY OUT 3
pulse is produced, which sets extended address bit 17.
The logic shown on Drawing TM11-0-17 is used to select the low- or high-order byte of the data register. This is
necessary because the MTCMA increments by 1 (byte addresses). Each time a byte transfer is completed, the
flip-flop is clocked by the NPR CLEAR BBSY signal. Initially, this flip-flop is cleared and produces the
La DATA BYTE output. After the first transaction, it is clocked and becomes set, thereby producing the
HI DATA BYTE output. The next transaction clocks it to the clear state. This process continues so that the
flip-flop produces alternate LO DATA BYTE and HI DATA BYTE sig~als to the data register until the desired
data transfer function is complete. When the function is complete, the controller CU RDY bit indicates that the
controller is ready to accept a new command. The CU RDY L signal direct clears the flip-flop; thus, any future
data transfers begin on even byte addresses.
5.8.6 Data Buffer Register (MTD)
The data buffer register is used as a temporary storage device during read and write operations. During read
operations, it stores characters from the tape prior to loading them into memory; during write operations, it stores
data prior to writing on the magnetic tape. A functional description of the data buffer register is given in

Paragraph 4.2.
The inputs to the data buffer are shown on Drawing TM 11-0-18. If a read operation is being performed, data is
loaded into the buffer from the tape transport data channels. Each channel is connected to one leg of an AND/
OR gate. The other leg to the gate is controlled by a flip-flop. The read operation (indicated by READ STB L)
sets this flip-flop. The high (1) side of the flip-flop qualifies four of the AND/OR gates to produce the
DATA BFR IN BIT H signals for bits a through 3. The low (0) side of the flip-flop produces the signals for bits
4 through 7. Thus, during a read operation, the data from the tape channels is gated through to the input of the
buffer register and strobed into the register by the DATA BFR STB signals. As shown on the data buffer drawing
(TMII-0-22), the first four bits are strobed in by the DATA BFR STB 1 signal; the second four bits are strobed
in by the DATA BFR STB 2 H signal.
During write operations, data from the bus is strobed into the data buffer register. The low byte is applied to one
series of gates, the high byte to another series of gates (Drawing TM 11-0-18). Each bus line is applied to one input
of a 2-input AND/OR gate. The other leg is qualified only if the appropriate byte has been selected. This selection
is determined by two AND gates. One is qualified if the current memory address is even (CMA 00 L), which indicates a low byte. The other is qualified if the current memory address is odd (CMA 00 H), which indicates a high
byte. The data from the bus lines is then strobed into the register in the same manner as before.

5-28

The data buffer output logic is shown on Drawings TM 11-0-16 and TM 11-0-11. The logic shown on Drawing
TM 11-0-16 is used when the output of the data buffer is to be applied to the bus. Each output of the data buffer
is applied to one leg of a 2-input AND gate. The other leg is qualified by either the HI DATA BYTE L or
LO DATA BYTE L signal, depending on which byte has been selected.
The logic shown on Drawing TMII-0-11 is used when the output of the data buffer is to be applied to the tape
unit for writing. When the core dump mode is not used, one byte in memory corresponds to one tape character.
In this instance, the output of the data buffer is gated through to the tape transport write lines. Data buffer bits
7 through 0 correspond to lines WDO through WD7, respectively.
When the core dump mode is used, one byte in memory corresponds to two tape characters. When the write
strobe (WRS) is issued, it sets the even character flip-flop (Drawing TM 11-0-13). This produces an EVEN CHAR H
pulse, which gates data buffer bits 0 through 3 to write lines WD7 through WD4 (Drawing TM 11-0-11). The flipflop then clears, and the""" EVEN CHAR H gates bits 4 through 7 to lines WD7 through WD4, respectively.
During normal read operations, all six tape data channels are read and gated through the data buffer input logic
for loading into the data buffer register. When the core dump mode is used, however, the logic operates in a different manner because one byte consists of two 4-bit characters. It is therefore necessary to read tape channels
0-3 twice, loading the first tape character into the low part of the buffer register and the second tape character
into the high part of the buffer. This is accomplished by the logic shown on drawing TM 11-0-18.
When the first tape character is read, the AND/NOR gates having channels 0-7 as inputs are all qualified by the
output of the READ STB flip-flop, and the data from the tape is gated through to become DATA BFR IN BITS
0-7. These bits are strobed into the data buffer register by DATA BFR STB 1 and 2 as shown on drawing TMll0-22. Up to this time, data has been read from the tape in a normal manner.
When the next tape character is read, the first set of AND/NOR gates is still qualified and produces DATA BFR
IN BITS 0-3. However, these bits are not loaded into the buffer register, because the required strobe signal is no
longer present. The low part of the buffer, thus, contains data read from channels 0-3 of the previous tape character.
The second series of AND/NOR gates, which normally receives inputs from tape channels 4-7, are now inhibited
due to the CORE DUMP L signal. The other AND inputs to these gates, which receive data from tape channels
0-3, are now qualified by an enabling AND gate having CORE DUMP L as an input. As a result, this series of
gates causes the data from tape channels 0-3 to become DATA BFR IN BITS 4-7. These bits are strobed into
the high part of the buffer and override the data previously stored in this part of the buffer. Thus, the two 4-bit
characters are now in the buffer as a single 8-bit byte.

5.8.7 TUI0 Read Lines (MTRD)
The TUI 0 read lines are assigned a standard bus address and are activated by the address select logic. When these
lines are selected for use, data from the lines is gated to appropriate data bits on the bus, as shown on drawing
TM 11-0-16. The 16 bits that constitute the read lines are read-only bits with the exception of the character select
(CHAR SEL) and bad tape error generator (BTE GEN) bits (bits 14 and 13, respectively). Bits 15 through 13
are described below; bits 11 through 09 are unused; and the remaining bits are described in Paragraph 4.2.
Bit 15 is the timer bit, which is used for diagnostic purposes by measuring the time duration of the tape operations.
The timer logic is shown on drawing TM11-0-07. This logic produces the timer signal (TIMER H), which is a 100j1S signal with a 50-percent duty cycle.

5-29

Bit 14 is the character select bit, which is used to select the last character of a record that is to be loaded into the
data buffer. When this bit is loaded with ai, the last character loaded into the buffer is the LPC character for
both 7-channel and 9-channel tapes. When this bit is loaded with a 0, the last character loaded in the buffer is the
last data character for 7-channel tapes or the CRC character for 9-channel tapes.
Bit 13 is the bad tape error generator, which is used to check the bad tape error logic. When loaded with aI, this
bit sets the CV READY flip-flop, thereby causing a premature gap shutdown period. When this portion of the
tape is then read, it produces a bad tape error indication.
Bit 12 is the gap shutdown bit. It is a read-only bit and indicates a gap shutdown period when it is a 1.
Data on the TV 10 read lines is gated to the bus by the logic shown on drawing TM 11-0-16. When the read lines
are selected for use (SEL 5 IN L), an inverter output qualifies one leg of a series of gates. The other leg of each
gate is connected to one of the channels in the tape transport. The output of these gates are then fed through
drivers to the bus.
5.9 TAPE CONTROL
The TM 11 Controller provides various tape control functions. These functions are: unit selection, function control, ready control, start control, and tape motion control. Each of these functions is described in detail in subsequent paragraphs.
5.9.1 Unit Select
The unit select logic determines the tape unit to be used for the selected function. Up to eight individual tape
units may be used with a single TM 11 Controller; however, only one tape unit may be selected for program control at any given time.
The number of the tape unit (0 through 7) to be selected is represented by a 3-bit number, generated by three
flip-flops (bits 10 through 08) in the command register as shown on drawing TMII-O-12.
The number of the desired tape unit is loaded into the command register from bus data lines DIO, D09, and D08.
If the command register has been selected for use (SEL 1 OUT HI), then the three unit flip-flops are set or cleared,
dependent on the bus input data. The flip-flop outputs are then applied to a decoder in the master tape transport
and to the register read lines.
The outputs of the three flip-flops are also applied 10 three additional flip-flops that provide signals for the motion
controllogic (refer to Paragraph 5.9.5).
5.9.2 Function Control
The function control logic specifies the command to be performed by the selected tape unit. Anyone of eight
functions can be selected for a given tape unit. A detailed description of each of these functions is given in Table
5-1.
The number of the function (0 through 7) to be selected is represented by a 3-bit number, generated by three
flip-flops (bits 03 through 0 I) in the command register as shown on drawing TM 11-0-09.
The number of the desired function is loaded into the command register from bus data lines D03, D02, and DOL
If the command register has been selected for use (SEL 1 OUT LO), then the three function flip-flops are set or
cleared, dependent on the bus input data. The outputs of these flip-flops are applied to a binary-to-octal decoder
to provide the necessary function signal.

5-30

5.9.3 Ready and Start Control
The TM 11 ready and start control circuits basically consist of the logic associated with two bits in the command
register. The ready logic is controlled by the CU READY bit (bit 07) and is described in detail in Paragraph
5.8.2.6. The start control logic is the GO bit (bit 00) and is described in Paragraph 5.8.2.10.
5.9.4 Tape Unit Motion Control
The master tape transport can accept and execute any command during the settle down (SDWN) period, unless
the command is to the same tape unit issuing the SDWN period and is in a direction opposite to the present direction of tape travel. If these two conditions exist, the SDWN period must be over and all tape motion stopped before the command can be executed. These two restrictions are handled by the tape unit motion control logic
(drawing TMII-0-07).
The key gate in this logic is the OR gate that produces the ENB SDWN GO L pulse. Whenever this pulse is produced, it is used by the start tape control logic (drawing TMI1-0-06) to produce the signals needed for execution
of the command. One leg of the OR gate is true if the same tape unit has not been selected; the other leg is true
if the direction implied in the new command is not different from the present direction. Therefore, the only time
that this gate is completely inhibited and the command cannot be executed until the end of SOWN time is when
both of the restrictions are present.
The tape motion control logic compares the unit select bit signals with the new unit select bits loaded into the
command register. If these bits are identical (indicating that the same tape unit is being selected), input gating to
the SAME TU flip-flop is not qualified, and the flip-flop is set to produce the SAME TU H signal. The 0 side of
the flip-flop is low and inhibits one leg of the output OR gate.
If, however, the comparison of the unit select bits indicates that a different tape unit has been selected, the OR
gates are qualified, the flip-flop remains cleared, and the ENB SOWN GO L signal is produced by the output OR
gate regardless of the level of the other leg.
If the new command implies that the tape is moving in the same direction, then the DIF DIR flip-flop remains
cleared, and the ENB SDWN GO L signal is sent to the start logic so that the command can be executed. If, however, the command implies a different direction, then the flip-flop is set and produces the OIF OIR H pulse. The
o side of the flip-flop goes low and inhibits one leg of the output OR gate. If the other leg of the OR gate has
been inhibited by the SAME TV flip-flop, then the command cannot be executed until SOWN is complete.

As an example of the direction logic, assume that a tape space reverse command has been executed, thereby making
the SPACE REV L signal true. This causes the associated flip-flop to be set, qualifying one leg of an ANO/NOR
gate. If the new command is a reverse or rewind function, both bits DOl Hand D03 H are true and the other input to the AND/NOR gate is not qualified. Therefore, the DIF DIR flip-flop remains cleared, because the new
command is in the same direction as the previous command.
If, however, the new function command indicates a different direction (such as a write command which implies
forward direction), either DOl H or D03 H is false, the other leg of the AND/NOR gate is now qualified, and the
DIF DIR flip-flop is set. The 0 side of the flip-flop goes low, there by inhibiting one leg of the output OR gate.
Note that the only time both DOl Hand D03 H aretrue is when a space reverse (octal 5) or rewind (octal 7) command is issued.

5-31

5.10 TIMING DIAGRAMS
Timing diagrams of various tape operations are shown in Figures 5-7 through 5-14. These diagrams portray specific tape operations such as reading a record of three data characters, reading a record of two tape characters in
the core dump mode, etc. The purpose of these diagrams is to illustrate overall TM 11 operation as described in
previous paragraphs.

SEL 2 OUT LO H

000 H

GO BIT H

GO STROBE 1 H

GO STROBE 2 H

-+______-+......

SET

+-_______---'

SELR L

+-_____.._... ...;~_____+~-----------r- -- ----- - --------

ILC

H __

__________

CU READY H
CUR DEL H _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _ _ ____

--.;~

11-0382

Figure 5-7 Start of Tape Operation

CU READY H

LPC H ________-1'

J~--__I,.I_I

SOW N H --------II_--++"

___..."n...._____I...Id

_ _ _

n. . __

'--_---JI--_ _ _ _.....

-'~L.

_ _ _ _ _ _ _ __

-'nL...-___

-"u/_________

GO~I---_+--'L..---II--------'n....--~ind/~-----------MTBRC ____~7~7~7~77~5~-~~--~7~7~7~77~6~---L--~7~7~7~7~77~-__~_ _ _~OO~O~O~O~O__
"-0385

Figure 5-8 Spacing Forward Three Records

5-32

CU READY H

LPS H

SOWN H

GO H

MTBRC
11-0387

Figure 5-9 Spacing Reverse Three Records

READY

LPC H - - - - - - f

SOWN H

GO H

BTE

MTBRC

----..,;'~----+-'

-----~/~-~~-------

ERR H
11-0386

Figure 5-10 Spacing Forward Three Records, Bad Tape Error
Appearing in First Record

5-33

CU READY H

1--28JJS--j
RDS

H-----I/~

NPR ENB H _ _ _ _

-I,~

MASTER H _ _ _ _

Cl. R

-Ij~

BB S Y H _______

;()'/~

_____

MTBRC __________7_7_7__
12_3__~______L_~---~--7-7-7-1-2-6------------______-+__

MTCMA _______~1~23~12~3__~_~~___L_~~~~_'~2~3~1~2~6____________~~___

CRCS _____________________________________

,...-,

CRCE _____________________________________ I __ I ______________
~

LPCS _________________________________________

~--------

r-"

LPCE _______________________________________________________I __ I ____________
~,

r-,

r--,

,.-,

I
I
I
I
I
I
I
I
I
I
VPE ______-I~-~~~~~~~--~{~~~~---~I,i~'-I~~I---_{')I~_~I
_ _ _ _ _ _ ___
I
I
I
I
;'/
// I
//
1'-0383

Figure 5-11 Reading Record of Three Data Characters

5-34

CU READY H

GO H

EVEN CHAR H

RDS H - - - - - 1 / /

NPR INT H - - - - - 1 /

,I_'______

--I~--.....J

CLR BBSY H -----I/,I-'--------Ir-----~I---------------~

MTBRC

777123

777124

MTCMA _ _ _ _ _ _ _ _ _1_2_3_12_3_ _ _ _ _ _ _ _~_~--1-2~3-12-4---------+_

CRe S _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

LPCS __________________________-------------------~

READ STB H

------------~~JLI_/----------Figure 5-12 Reading Record of Two Tape Characters
in Core Dump Mode

5-35

CU READY H

WRS H

GO STROBE 2H

NPR INT H

MASTER H

CLR BBSY H

MTBRC 777775

OVERFLOW H

WDR

RDS H

CRCS

r- - ,
CRC ERROR

LPCS

-----...,
:
LPC ERROR

)J.

,-,

,--.,
VPC ERROR

,-..,

r-,
//

I 1/

,-I
I

..,

I
I
11-0384

Figure 5-13 Writing Record of Three Data Characters

5-36

CU READY H

GO STROBE 2 H

EVEN CHAR H

1-----28•• ------l

WRS H-+__~----~

.
~~(~--------------------------------------------

NPR INT H +-__---'

CLR BBSY H+-______~I~~------------~---------------------------------------------------------__
______-+__________________________________________________________
MTBRC~

MTCMA~

OVERFLOW

~~~~~~~

~~~~1~23~1~2~4~

______

__________________________________________________________

_~_ _ _-'

WDR

I---- 2BlJs-........f·-------- 64 j.1s - - - - -......I·....--84IJ s---l

RDSH------fl~~/

CRCS _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

LPCS ________________________________________________

"-0389

Figure 5-14 Writing Record of Two Tape Characters
in Core Dump Mode

5-37

CHAPTER 6
MODULE DESCRIPTION

6.1 INTRODUCfION
This chapter provides infonnation on the logic modules used in the TM 1 I DECmagtape Controller. The position
of the modules within the mounting box is shown on Drawing TMll-O-02.
A list of all TMll Controller modules is presented in Table 6-1. This table lists the modules in numerical order,
the quantity of each type used in the system, and the name of the module. The last column indicates the DEC
document containing the detailed description of that particular module.
Note that it is beyond the scope of this manual to provide information on any of the modules used in the Master
Tape Transport logic.
6.2 DEC LOGIC
Except for cable and jumper modules, all of the modules used in the TM 11 Controller are M-Series logic modules.
The M-Series are high-speed, monolithic integrated circuit modules, employing TTL logic (transistor-transistor
logic). These circuits provide high speed, high fanout, large capacitance drive capability, and excellent noise
margins.
A general description of DEC logic and detailed circuit descriptions of TTL logic gates is provided in the 1971
DEC Logic Handbook. The symbology used with all PDP-II logic drawings is shown and explained in the PDP-11
Conventions Manual, DEC-ll-HR6B-D.
6.3 MEASUREMENT DEFINITIONS
Timing is measured with the input driven by a gated pulse amplifier of the series under test and with the output
loaded with gates of the same series. Percentages are assigned as follows: 0 percent is the initial steady-state level,
100 percent is the final steady-state level, regardless of the direction of change.
Input/output delay is the time difference between input change and output change, measured from 50 percent
input change to 50 percent output change. Rise and fall delays for the same module are usually specified separately. Rise time and fall time is measured from 10 percent to 90 percent of waveform change, rising or falling.
6.4 LOADING
Input loading and output driving are specified in unit loads, where one unit load is 1.6 rnA by definition. The
inputs to low-speed gates usually draw one unit load. High-speed gates draw 1-1/4 unit loads, or 2 rnA.

6-1

Table 6-1
Module Utilization
Module Number

Title

Quantity Used

Reference

MIOS
MIll
MIl2
MII3
MllS
MII7
MI21
MI27
MI49
MI63

I
6
3
6
2
I
2
3
4
I

Address Selector
Inverter
NOR Gate
Ten 2-input NAND Gates
Eight 3-input NAND Gates
Six 4-input NAND Gates
AND/NOR Gate
2-2-2-3 AND/NOR Gate
9x2 NAND Wired OR Matrix
Dual Binary-to-Octal Decoder

1
2
2
2
2
2
2

M203
M20S
M216
M239

I
2
S
I

Eight Reset/Set Flip-Flops
Five "D" Flip-Flops
Six Flip-Flops
Three 4-bit Counter Registers

M304
M307

2
1

Four One-Shot Delays
Integrating One-Shot

M627

NAND Power Amplifier

G736

Jumper Module

M7821
M784
M78S
M79S
M796
M797
M798

I
1
1
2
1
1
1

Interrupt Control
Unibus Receiver
Unibus Transceiver
Word Count and Bus Address Register
Unibus Master Control
Register Selection
Unibus Drivers

1
1
1
1
1
1
1

REFERENCES

Chapter 3 of Unibus Interface Manual, Second Edition, DEC-II-HIAB-D.

DEC Logic Handbook, 1971 Edition.

6-2

APPENDIX A
MASTER TAPE TRANSPORT SIGNALS

A.l SIGNALS FROM MASTER TO TMll CONTROLLER
Mnemonic

Name

RDO - RD7

Read data signals

RDP

Read parity bit

SDWN

Tape settle down. This is the time between a stop command and the time
when the unit actually stops.

TUR

Tape unit ready. This signal is true when the selected tape unit is stopped,
and SELR is true.

SELR

Select remote. This is true when unit is selected and is on-line.

RWS

Rewind status. This is true when selected unit is rewinding.

7CH

7-channel. True during 7-channel operation.

WRL

Write lock. Prevents writing on tape.

BOT

Beginning of tape

EOT

End of tape

WRS

Write strobe. Requests a character for writing.

RDS

Read strobe. Present for both read and write operations.

FMK

File mark

CRCS

CRC strobe. Appears with CRC character.

LRCS

LRC strobe. Appears with LPC character.

VPE

Vertical parity check error. Sampled with RDS.

LReE

Longitudinal parity check error. Sampled with LPCS.

A-I

A.2 SIGNALS FROM TM 11 CONTROLLER TO MASTER

Name

Mnemonic

WDO - WD7

Write data lines

SET

Required to start any tape operation (derivative of GO command).

FWD

Tape forward

REV

Tape reverse

RWD

Tape rewind

WRE

Write enable

PEVN

Even parity

DEN 8

Density bit - true for 800 bpi, 7-channel
true for 800 bpi, 9-channel
false for 200 bpi, 7-channel
false for 556 bpi, 7-channel

DEN 5

Density bit - true for 556 bpi, 7-channel
true for 800 bpi, 9-channel
false for 200 bpi, 7-channel
false for 800 bpi, 7-channel

WFMK

Write file mark

WXG

Write-extended-IRG gap. True for both write-extended-IRG and WFMK
functions.

~~~~}

Tape unit select

SEL 2
WDR

Write data ready

CINIT

Initialize

A-2

TM11DECMAGTAPESYSTEM
DEC-II-HTMAA-D-D

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