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User Manual: Digital Equipment Corporation PDP-8 Simulator ation

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PDP-8 Simulator Usage
01-Dec-08
COPYRIGHT NOTICE
The following copyright notice applies to the SIMH source, binary, and documentation:
Original code published in 1993-2008, written by Robert M Supnik
Copyright (c) 1993-2008, Robert M Supnik
Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify, merge,
publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or
substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL ROBERT M SUPNIK BE LIABLE FOR
ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
Except as contained in this notice, the name of Robert M Supnik shall not be used in
advertising or otherwise to promote the sale, use or other dealings in this Software
without prior written authorization from Robert M Supnik.

1
2

Simulator Files ............................................................................................................. 3
PDP-8 Features ........................................................................................................... 3
2.1
CPU ...................................................................................................................... 5
2.2
TSC8-75 ETOS Timeshare Control (TSC)............................................................ 6
2.3
Programmed I/O Devices ..................................................................................... 6
2.3.1
PC8E Paper Tape Reader (PTR) .................................................................. 6
2.3.2
PC8E Paper Tape Punch (PTP) .................................................................... 7
2.3.3
KL8E Terminal Input (TTI) ............................................................................. 7
2.3.4
KL8E Terminal Output (TTO)......................................................................... 8
2.3.5
LE8E Line Printer (LPT)................................................................................. 8
2.3.6
DK8E Line-Frequency Clock (CLK) ............................................................... 9
2.3.7
KL8JA Additional Terminals (TTIX, TTOX) .................................................... 9
2.3.8
TD8E/TU56 DECtape (TD) .......................................................................... 10
2.3.9
TA8E/TA60 Cassette Tape (CT).................................................................. 11
2.4
Moving Head Disks............................................................................................. 12
2.4.1
RK8E Cartridge Disk (RK) ........................................................................... 12
2.4.2
RL8A Cartridge Disk (RL) ............................................................................ 12
2.5
RX8E/RX01, RX28/RX02 Floppy Disk (RX) ....................................................... 13
2.6
Fixed Head Disks................................................................................................ 14
2.6.1
RF08/RS08 Fixed Head Disk (RF) .............................................................. 14
2.6.2
DF32/DS32 Fixed Head Disk (RF) .............................................................. 15
2.7
TC08/TU56 DECtape (DT) ................................................................................. 16
2.8
TM8E Magnetic Tape (MT) ................................................................................. 17
3 Symbolic Display and Input........................................................................................ 17

This memorandum documents the PDP-8 simulator.

1 Simulator Files
sim/

scp.h
sim_console.h
sim_defs.h
sim_fio.h
sim_rev.h
sim_sock.h
sim_tape.h
sim_timer.h
sim_tmxr.h
scp.c
sim_console.c
sim_fio.c
sim_sock.c
sim_tape.c
sim_timer.c
sim_tmxr.c

sim/pdp8/

pdp8_defs.h
pdp8_cpu.c
pdp8_ct.c
pdp8_df.c
pdp8_dt.c
pdp8_lp.c
pdp8_mt.c
pdp8_pt.c
pdp8_rf.c
pdp8_rk.c
pdp8_rl.c
pdp8_rx.c
pdp8_sys.c
pdp8_td.c
pdp8_tsc.c
pdp8_tt.c
pdp8_ttx.c

2 PDP-8 Features
The PDP-8 simulator is configured as follows:
device names(s)

simulates

CPU
TSC
PTR,PTP
TTI,TTO
TTIX,TTOX

PDP-8/E CPU with 4KW-32KW of memory
KE8E extended arithmetic element (EAE)
KM8E memory management and timeshare control
TSC8-75 ETOS operating system timeshare control
PC8E paper tape reader/punch
KL8E console terminal
KL8JA additional terminals

LPT
CLK
RK
RF
DF
RL
RX

LE8E line printer
DK8E line frequency clock (also PDP-8/A compatible)
RK8E/RK05 cartridge disk controller with four drives
RF08/RS08 fixed head disk controller with 1-4 platters
DF32/DS32 fixed head disk controller with 1-4 platters
RL8A/RL01 cartridge disk controller with four drives
RX8E/RX01, RX28/RX02 floppy disk controller with two
drives
TC08/TU56 DECtape controller with eight drives
TD8E/TU56 DECtape controller with two drives
TM8E/TU10 magnetic tape controller with eight drives
TA8E/TU60 cassette tape controller with two drives

DT
TD
MT
CT

Most devices can be disabled or enabled, by the commands:
SET  DISABLED
SET  ENABLED
The simulator allows most device numbers to be changed, by the command:
SET  DEV=
The PDP-8 can support only one of the set {DF32, RF08, RL8A} using the default device numbers, since
they all use device numbers 60-61. The default is the RF08. To change the disk at device numbers 60-61:
SET RF DISABLED
SET DF ENABLED, or
SET RL ENABLED

disable RF08
enable DF32
enable RL8A

The PDP-8 can only support one of the set {TC08, TD8E} using the default device numbers, since both use
device number 77. The default is the TC08. To change the DECtape controller to the TD8E:
SET DT DISABLED
SET TD ENABLED

disable TC08
enable TD8E

The PDP-8 can only support one of the set {TM8E, TA8E} using the default device numbers, since both use
device number 70. The default is the TM8E. To change the device at device number 70:
SET MT DISABLED
SET CT ENABLED

disable TM8E
enable TA8E

Alternately, the device conflict can be eliminated by changing device numbers:
SET
SET
SET
SET
SET
SET

RL
RL
TD
TD
CT
CT

DEV=50
ENA
DEV=74
ENA
DEV=73
ENA

However, devices can only be BOOTed with their default device numbers.
The PDP-8 simulator implements several unique stop conditions:
-

If an undefined instruction (unimplemented IOT or OPR) is decoded, and STOP_INST is set
If a simulated DECtape runs off the end of its reel

The LOAD command supports both RIM format and BIN format tapes. If the file extension is .RIM, or the r
switch is specified with LOAD, the file is assumed to be RIM format; if the file extension is not .RIM, or the -b
switch is specified, the file is assumed to be BIN format.

2.1 CPU
The only CPU options are the presence of the EAE and the size of main memory; the memory extension
and time-share control is always included, even if memory size is 4K.
SET
SET
SET
SET
SET
SET
SET
SET
SET
SET

CPU
CPU
CPU
CPU
CPU
CPU
CPU
CPU
CPU
CPU

EAE
NOEAE
4K
8K
12K
16K
20K
24K
28K
32K

enable EAE
disable EAE
set memory size
set memory size
set memory size
set memory size
set memory size
set memory size
set memory size
set memory size

=
=
=
=
=
=
=
=

4K
8K
12K
16K
20K
24K
28K
32K

If memory size is being reduced, and the memory being truncated contains non-zero data, the simulator
asks for confirmation. Data in the truncated portion of memory is lost. Initial memory size is 32K.
CPU registers include the visible state of the processor as well as the control registers for the interrupt
system.
name

size

comments

PC
AC
MQ
L
SR
IF
DF
IB
SF
UF
UB
SC
GTF
EMODE
ION
ION_DELAY
CIF_DELAY
PWR_INT
UF_INT
INT
DONE
ENABLE
PCQ[0:63]

15
12
12
1
12
3
3
3
7
1
1
5
1
1
1
1
1
1
1
15
15
15
15

STOP_INST
WRU

1
8

program counter, including IF as high 3 bits
accumulator
multiplier-quotient
link
front panel switches
instruction field
data field
instruction field buffer
save field
user mode flag
user mode buffer
EAE shift counter
EAE greater than flag
EAE mode (0 = A, 1 = B)
interrupt enable
interrupt enable delay for ION
interrupt enable delay for CIF
power fail interrupt
user mode violation interrupt
interrupt pending flags
device done flags
device interrupt enable flags
PC prior to last JMP, JMS, or interrupt;
most recent PC change first
stop on undefined instruction
interrupt character

The CPU attempts to detect when the simulator is idle. When idle, the simulator does not use any resources
on the host system. Idle detection is controlled by the SET IDLE and SET NOIDLE commands:
enable idle detection
disable idle detection

SET CPU IDLE
SET CPU NOIDLE

Idle detection is disabled by default. At present, the CPU is considered idle if it is executing a KSF/JMP *-1
loop with interrupts disabled (OS/8, DMS-8) or a JMP * loop (TSS/8).
The CPU can maintain a history of the most recently executed instructions. This is controlled by the SET
CPU HISTORY and SHOW CPU HISTORY commands:
SET CPU HISTORY
SET CPU HISTORY=0
SET CPU HISTORY=n
SHOW CPU HISTORY
SHOW CPU HISTORY=n

clear history buffer
disable history
enable history, length = n
print CPU history
print first n entries of CPU history

The maximum length for the history is 65536 entries.

2.2 TSC8-75 ETOS Timeshare Control (TSC)
ETOS is a timeshared operating system for the PDP-8, providing multiple virtual OS/8 environments for up
to 32 users. It requires a special timeshare control option, the TSC8-75. The TSC8-75 is normally disabled;
to run ETOS, it must be enabled with the command:
SET TSC ENABLED
The TSC8-75 implements these registers:
name

size

comments

IR
PC
CDF
ENB
INT

12
12
1
1
1

most recently trapped instruction
PC of most recently trapped instruction
1 if trapped instruction is CDF, 0 otherwise
interrupt enable flag
interrupt pending flag

Except for operation of ETOS, the TSC8-75 should be left disabled.

2.3 Programmed I/O Devices
2.3.1 PC8E Paper Tape Reader (PTR)
The paper tape reader (PTR) reads data from a disk file. The POS register specifies the number of the next
data item to be read. Thus, by changing POS, the user can backspace or advance the reader.
The paper tape reader supports the BOOT command. BOOT PTR copies the RIM loader into memory and
starts it running.
The paper tape reader implements these registers:
name

size

comments

BUF
DONE
ENABLE
INT
POS
TIME
STOP_IOE

8
1
1
1
32
24
1

last data item processed
device done flag
interrupt enable flag
interrupt pending flag
position in the input file
time from I/O initiation to interrupt
stop on I/O error

Error handling is as follows:
error

STOP_IOE

processed as

not attached

1
0

report error and stop
out of tape

end of file

1
0

report error and stop
out of tape

OS I/O error

x

report error and stop

2.3.2 PC8E Paper Tape Punch (PTP)
The paper tape punch (PTP) writes data to a disk file. The POS register specifies the number of the next
data item to be written. Thus, by changing POS, the user can backspace or advance the punch.
The paper tape punch implements these registers:
name

size

comments

BUF
DONE
ENABLE
INT
POS
TIME
STOP_IOE

8
1
1
1
32
24
1

last data item processed
device done flag
interrupt enable flag
interrupt pending flag
position in the output file
time from I/O initiation to interrupt
stop on I/O error

Error handling is as follows:
error

STOP_IOE

processed as

not attached

1
0

report error and stop
out of tape

OS I/O error

x

report error and stop

2.3.3 KL8E Terminal Input (TTI)
The terminal interfaces (TTI, TTO) can be set to one of four modes, KSR, 7B, 7B, or 8B:
mode

input characters

output characters

KSR

lower case converted
to upper case,
high-order bit set

lower case converted to upper case,
high-order bit cleared,
non-printing characters suppressed

7P

high-order bit cleared

7B
8B

high-order bit cleared
no changes

high-order bit cleared,
non-printing characters suppressed
high-order bit cleared
no changes

The default mode is KSR.
The terminal input (TTI) polls the console keyboard for input. It implements these registers:
name

size

comments

BUF
DONE
ENABLE
INT
POS
TIME

8
1
1
1
32
24

last data item processed
device done flag
interrupt enable flag
interrupt pending flag
number of characters input
input polling interval (if 0, the keyboard
is polled synchronously with the clock)

2.3.4 KL8E Terminal Output (TTO)
The terminal output (TTO) writes to the simulator console window. It implements these registers:
name

size

comments

BUF
DONE
ENABLE
INT
POS
TIME

8
1
1
1
32
24

last data item processed
device done flag
interrupt enable flag
interrupt pending flag
number of characters output
time from I/O initiation to interrupt

2.3.5 LE8E Line Printer (LPT)
The line printer (LPT) writes data to a disk file. The POS register specifies the number of the next data item
to be read or written. Thus, by changing POS, the user can backspace or advance the printer.
The line printer implements these registers:
name

size

comments

BUF
ERR
DONE
ENABLE
INT
POS
TIME

8
1
1
1
1
32
24

last data item processed
error status flag
device done flag
interrupt enable flag
interrupt pending flag
position in the output file
time from I/O initiation to interrupt

Error handling is as follows:
error
not attached

STOP_IOE
1
0

processed as
report error and stop
out of paper

OS I/O error

x

report error and stop

2.3.6 DK8E Line-Frequency Clock (CLK)
The real-time clock (CLK) frequency can be adjusted as follows:
SET CLK 60HZ
SET CLK 50HZ

set frequency to 60Hz
set frequency to 50Hz

The default is 60Hz.
The clock implements these registers:
name

size

comments

DONE
ENABLE
INT
TIME

1
1
1
24

device done flag
interrupt enable flag
interrupt pending flag
clock interval

The real-time clock autocalibrates; the clock interval is adjusted up or down so that the clock tracks actual
elapsed time.

2.3.7 KL8JA Additional Terminals (TTIX, TTOX)
The additional terminals consist of two independent devices, TTIX and TTOX. The entire set is modeled as
a terminal multiplexer, with TTIX as the master controller. The additional terminals perform input and output
through Telnet sessions connected to a user-specified port. The ATTACH command specifies the port to be
used:
ATTACH TTIX 

set up listening port

where port is a decimal number between 1 and 65535 that is not being used for other TCP/IP activities.
The additional terminals can be set to one of four modes: UC, 7P, 7B, or 8B.
mode

input characters

output characters

UC

7P

lower case converted
to upper case,
high-order bit cleared
high-order bit cleared

7B
8B

high-order bit cleared
no changes

lower case converted to upper case,
high-order bit cleared,
non-printing characters suppressed
high-order bit cleared,
non-printing characters suppressed
high-order bit cleared
no changes

The default mode is UC. Finally, each line supports output logging. The SET TTOXn LOG command
enables logging on a line:
SET TTOXn LOG=filename

log output of line n to filename

The SET TTOXn NOLOG command disables logging and closes the open log file, if any.

Once TTIX is attached and the simulator is running, the terminals listen for connections on the specified
port. They assume that the incoming connections are Telnet connections. The connections remain open
until disconnected either by the Telnet client, a SET TTIX DISCONNECT command, or a DETACH TTIX
command.
Other special commands:
SHOW TTIX CONNECTIONS
SHOW TTIX STATISTICS
SET TTOXn DISCONNECT

show current connections
show statistics for active connections
disconnects the specified line.

The input device (TTIX) implements these registers:
name

size

comments

BUF[0:3]
DONE
ENABLE
INT
TIME
TPS

8
4
4
4
24
10

input buffer, lines 0 to 3
device done flags (line 0 rightmost)
interrupt enable flag
interrupt pending flag
initial polling interval
polls per second after calibration

The output device (TTOX) implements these registers:
name

size

comments

BUF[0:3]
DONE
ENABLE
INT
TIME[0:3]

8
4
4
4
24

last data item processed, lines 0-3
device done flag (line 0 rightmost)
interrupt enable flag
interrupt pending flag
time from I/O initiation to interrupt,
lines 0-3

The additional terminals do not support save and restore. All open connections are lost when the simulator
shuts down or TTIX is detached.

2.3.8 TD8E/TU56 DECtape (TD)
The TD8E is a programmed I/O, non-interrupt controller, supporting two DECtape drives (0 and 1). The
TD8E simulator puts a high burden on the host processor, because tape activity is simulated a line (3b) at a
time. Unless the PDP-8 software requires the TD8E, the TC08 should be used to simulate DECtapes. The
TD8E is disabled by default.
TD8E options include the ability to make units write enabled or write locked.
SET TDn LOCKED
SET TDn WRITEENABLED

set unit n write locked
set unit n write enabled

Units can also be set ENABLED or DISABLED. The TD8E supports the BOOT command, but only for unit 0.
The TD8E supports supports PDP-8 format, PDP-11 format, and 18b format DECtape images. ATTACH
assumes the image is in PDP-8 format; the user can force other choices with switches:
-s
-f

PDP-11 format
18b format

-a

autoselect based on file on file size

The TD8E controller is a data-only simulator; the timing and mark track, and block header and trailer, are not
stored. Thus, read always produces standard values for mark track, header, and trailer words, and write
throws mark track, header, and trailer words into the bit bucket.
The TD8E controller implements these registers:
name

size

comments

TDCMD
TDDAT
TDMTK
TDSLF
TDQLF
TDTME
TDQL
LTIME
DCTIME
POS[0:1]
STATT[0:1]
STOP_OFFR

4
12
6
1
1
1
2
31
31
32
18
1

command register
data register
mark track register
single line flag
quad line flag
timing error flag
quad line counter
time between lines
time to decelerate to a full stop
position, in lines, units 0 and 1
unit state, units 0 and 1
stop on off-reel error

The LTIME parameter should not be changed, or OS/8 may fail to run correctly. The DCTIME parameter
should always be at least 100 times greater than LTIME. Acceleration time is 75% of deceleration time.

2.3.9 TA8E/TA60 Cassette Tape (CT)
The TA8E is a programmed I/O controller supporting two cassette drives (0 and 1). The TA8E can be used
with the MCPIP program under OS/8, and with the CAPS-8 operating system. Cassettes are simulated as
magnetic tapes with a fixed capacity (93,000 characters). The tape format is always SimH standard. The
TA8E is disabled by default.
TA8E options include the ability to make units write enabled or write locked.
SET CTn LOCKED
SET CTn WRITEENABLED

set unit n write locked
set unit n write enabled

Units cannot be set ENABLED or DISABLED. The TA8E supports the BOOT command, but only for CAPS-8,
and only for unit 0.
The TA8E controller implements these registers:
name

size

comments

CTSRA
CTSRB
CTDB
CTDF
RDY
WLE
WRITE
INT
BPTR
BLNT
STIME

8
8
8
1
1
1
1
1
17
17
24

status register A
status register B
data buffer
data flag
ready flag
write lock error
TA60 write operation flag
interrupt request
buffer pointer
buffer length
operation start time

CTIME
STOP_IOE
POS[0:1]

24
1
32

character latency
stop on I/O errors flag
position, units 0-1

Error handling is as follows:
error

processed as

not attached

tape not ready; if STOP_IOE, stop

end of file

bad tape

OS I/O error

CRC error; if STOP_IOE, stop

2.4 Moving Head Disks
2.4.1 RK8E Cartridge Disk (RK)
RK8E options include the ability to make units write enabled or write locked:
SET RKn LOCKED
SET RKn WRITEENABLED

set unit n write locked
set unit n write enabled

Units can also be set ENABLED or DISABLED. The RK8E supports the BOOT command.
The RK8E implements these registers:
name

size

RKSTA
RKCMD
RKDA
RKMA
BUSY
INT
STIME
RTIME
STOP_IOE

12
12
12
12
1
1
24
24
1

comments
status
disk command
disk address
current memory address
control busy flag
interrupt pending flag
seek time, per cylinder
rotational delay
stop on I/O error

Error handling is as follows:
error

STOP_IOE

processed as

not attached

1
0

report error and stop
disk not ready

end of file

x

assume rest of disk is zero

OS I/O error

x

report error and stop

2.4.2 RL8A Cartridge Disk (RL)
RL8A options include the ability to make units write enabled or write locked:
SET RLn LOCKED

set unit n write locked

SET RLn WRITEENABLED

set unit n write enabled

Units can also be set ENABLED or DISABLED. The RL8A supports the BOOT command, but only for unit 0.
The RL8A implements these registers:
name

size

comments

RLCSA
RLCSB
RLMA
RLWC
RLSA
RLER
RLSI
RLSI1
RLSI2
RLSIL
INT
DONE
ERR
STIME
RTIME
STOP_IOE

12
12
12
12
6
12
16
16
16
1
1
1
1
1
1
1

control/status A
control/status B
memory address
word count
sector address
error flags
silo top word
silo second word
silo third word
silo read left/right flag
interrupt request
done flag
composite error flag
seek time, per cylinder
rotational delay
stop on I/O error

Error handling is as follows:
error

STOP_IOE

processed as

not attached

1
0

report error and stop
disk not ready

end of file

x

assume rest of disk is zero

OS I/O error

x

report error and stop

2.5 RX8E/RX01, RX28/RX02 Floppy Disk (RX)
The RX can be configured as an RX8E with two RX01 drives, or an RX28 with two RX02 drives:
SET RX RX8E
SET RX RX28

set controller to RX8E/RX01
set controller to RX28/RX02

The controller is set to the RX8E by default. The RX28 is not backwards-compatible with the RX8E and will
not work with the standard OS/8 V3D floppy disk driver.
RX8E options include the ability to set units write enabled or write locked:
SET RXn LOCKED
SET RXn WRITEENABLED

set unit n write locked
set unit n write enabled

RX28 options include, in addition, the ability to set the unit density to single density, double density, or
autosized; autosizing is the default:
SET RXn SINGLE
SET RXn DOUBLE

set unit n single density
set unit n double density

SET RXn AUTOSIZE

set unit n autosize

The RX8E and RX28 support the BOOT command.
The RX8E and RX28 implement these registers:
name

size

comments

RXCS
RXDB
RXES
RXTA
RXSA
STAPTR
BUFPTR
INT
DONE
ENABLE
TR
ERR
CTIME
STIME
XTIME
STOP_IOE
SBUF[0:255]

12
12
12
8
8
4
8
1
1
1
1
1
24
24
24
1
8

status
data buffer
error status
current track
current sector
controller state
buffer pointer
interrupt pending flag
device done flag
interrupt enable flag
transfer ready flag
error flag
command completion time
seek time, per track
transfer ready delay
stop on I/O error
sector buffer array

Error handling is as follows:
error

STOP_IOE

not attached

1
0

processed as
report error and stop
disk not ready

RX01 and RX02 data files are buffered in memory; therefore, end of file and OS I/O errors cannot occur.

2.6 Fixed Head Disks
With default device addressing, either the RF08 or the DF32 can be present in a configuration, but not both.

2.6.1 RF08/RS08 Fixed Head Disk (RF)
RF08 options include the ability to set the number of platters to a fixed value between 1 and 4, or to autosize
the number of platters:
SET
SET
SET
SET
SET

RF
RF
RF
RF
RF

1P
2P
3P
4P
AUTOSIZE

one platter (256K)
two platters (512K)
three platters (768K)
four platters (1024K)
autosized on ATTACH

The default is one platter.
The RF08 implements these registers:
name

size

comments

STA
DA
MA
WC
WLK
INT
DONE
TIME
BURST
STOP_IOE

12
20
12
12
32
1
1
24
1
1

status
current disk address
memory address (in memory)
word count (in memory)
write lock switches
interrupt pending flag
device done flag
rotational delay, per word
burst flag
stop on I/O error

The RF08 supports the BOOT command. The default bootstrap is for OS/8. To bootstrap the 4K Disk
Monitor, use the BOOT -D RF command.
The RF08 is a three-cycle data break device. If BURST = 0, word transfers are scheduled individually; if
BURST = 1, the entire transfer occurs in a single data break.
Error handling is as follows:
error

STOP_IOE

not attached

1
0

processed as
report error and stop
disk not ready

RF08 data files are buffered in memory; therefore, end of file and OS I/O errors cannot occur.

2.6.2 DF32/DS32 Fixed Head Disk (RF)
DF32 options include the ability to set the number of platters to a fixed value between 1 and 4, or to autosize
the number of platters:
SET
SET
SET
SET
SET

DF
DF
DF
DF
DF

1P
2P
3P
4P
AUTOSIZE

one platter (32K)
two platters (64K)
three platters (98K)
four platters (128K)
autosized on ATTACH

The default is one platter.
The DF32 implements these registers:
name

size

comments

STA
DA
MA
WC
WLK
INT
DONE
TIME
BURST
STOP_IOE

12
12
12
12
16
1
1
24
1
1

status, disk and memory address extension
low order disk address
memory address (in memory)
word count (in memory)
write lock switches
interrupt pending flag
device done flag
rotational delay, per word
burst flag
stop on I/O error

The DF32 supports the BOOT command. The default bootstrap is for OS/8. To bootstrap the 4K Disk
Monitor, use the BOOT -D DF command.
The DF32 is a three-cycle data break device. If BURST = 0, word transfers are scheduled individually; if
BURST = 1, the entire transfer occurs in a single data break.
Error handling is as follows:
error
not attached

STOP_IOE
1
0

processed as
report error and stop
disk not ready

DF32 data files are buffered in memory; therefore, end of file and OS I/O errors cannot occur.

2.7 TC08/TU56 DECtape (DT)
DECtapes drives are numbered 1-8; in the simulator, drive 8 is unit 0. TC08 options include the ability to
make units write enabled or write locked.
SET DTn LOCKED
SET DTn WRITEENABLED

set unit n write locked
set unit n write enabled

Units can also be set ENABLED or DISABLED. The TC08 supports the BOOT command, but only for unit 0.
The TC08 supports supports PDP-8 format, PDP-11 format, and 18b format DECtape images. ATTACH
assumes the image is in PDP-8 format; the user can force other choices with switches:
-s
-f
-a

PDP-11 format
18b format
autoselect based on file on file size

The TC08 controller is a data-only simulator; the timing and mark track, and block header and trailer, are not
stored. Thus, the WRITE TIMING AND MARK TRACK function is not supported; the READ ALL function
always returns the hardware standard block header and trailer; and the WRITE ALL function dumps nondata words into the bit bucket.
The DECtape controller implements these registers:
name

size

comments

DTSA
DTSB
INT
ENB
DTF
ERF
CA
WC
LTIME
DCTIME
SUBSTATE
POS[0:7]
STATT[0:7]
STOP_OFFR

12
12
1
1
1
1
12
12
31
31
2
32
31
1

status register A
status register B
interrupt pending flag
interrupt enable flag
DECtape flag
error flag
current address (memory location 7754)
word count (memory location 7755)
time between lines
time to decelerate to a full stop
read/write command substate
position, in lines, units 0 to 7
unit state, units 0 to 7
stop on off-reel error

It is critically important to maintain certain timing relationships among the DECtape parameters, or the
DECtape simulator will fail to operate correctly.
-

LTIME must be at least 6
DCTIME needs to be at least 100 times LTIME

Acceleration time is set to 75% of deceleration time.

2.8 TM8E Magnetic Tape (MT)
Magnetic tape options include the ability to make units write enabled or write locked.
SET MTn LOCKED
SET MTn WRITEENABLED

set unit n write locked
set unit n write enabled

Magnetic tape units can be set to a specific reel capacity in MB, or to unlimited capacity:
SET MTn CAPAC=m
SHOW MTn CAPAC

set unit n capacity to m MB (0 = unlimited)
show unit n capacity in MB

Units can also be set ENABLED or DISABLED.
The magnetic tape controller implements these registers:
name

size

comments

CMD
FNC
CA
WC
DB
STA
STA2
DONE
INT
STOP_IOE
TIME
UST[0:7]
POS[0:7]

12
12
12
12
12
12
6
1
1
1
24
24
32

command
function
memory address
word count
data buffer
main status
secondary status
device done flag
interrupt pending flag
stop on I/O error
record delay
unit status, units 0 to 7
position, units 0 to 7

Error handling is as follows:
error

processed as

not attached

tape not ready; if STOP_IOE, stop

end of file

bad tape

OS I/O error

parity error; if STOP_IOE, stop

3 Symbolic Display and Input

The PDP-8 simulator implements symbolic display and input. Display is controlled by command line
switches:
-a
-c
-t
-m

display
display
display
display

as ASCII character
as two packed sixbit characters
as two packed TSS/8 sixbit characters
instruction mnemonics

Input parsing is controlled by the first character typed in or by command line switches:
' or -a
" or -c
# or -t
alphabetic
numeric

ASCII character
two packed sixbit characters
two packed TSS/8 sixbit characters
instruction mnemonic
octal number

Instruction input uses standard PDP-8 assembler syntax. There are four instruction classes: memory
reference, IOT, field change, and operate.
Memory reference instructions have the format
memref {I} {C/Z} address
where I signifies indirect, C a current page reference, and Z a zero page reference. The address is an octal
number in the range 0 - 07777; if C or Z is specified, the address is a page offset in the range 0 - 177.
Normally, C is not needed; the simulator figures out from the address what mode to use. However, when
referencing memory outside the CPU (eg, disks), there is no valid PC, and C must be used to specify current
page addressing.
IOT instructions consist of single mnemonics, eg, KRB, TLS. IOT instructions may be or'd together
iot iot iot...
The simulator does not check the legality of the proposed combination. IOT's for which there is no opcode
may be specified as IOT n, where n is an octal number in the range 0 - 0777.
Field change instructions (CIF, CDF) have the format
fldchg field
where field is an octal number in the range 0 - 7. Field change instructions may be or'd together.
Operate instructions have the format
opr opr opr...
The simulator does not check the legality of the proposed combination. EAE mode A and B mnemonics
may be specified regardless of the EAE mode. The operands for MUY and DVI must be deposited explicitly.



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