North_Star_Z80A_Processor_Board_ZPB A_Rev_2_1977 North Star Z80A Processor Board ZPB A Rev 2 1977

North_Star_Z80A_Processor_Board_ZPB-A_Rev_2_1977 North_Star_Z80A_Processor_Board_ZPB-A_Rev_2_1977

User Manual: North_Star_Z80A_Processor_Board_ZPB-A_Rev_2_1977

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NORTH STAR

*

COMPUTERS,

INc.

2547 Ninth Street · Berk eley, Cali forni a 94710 • (4 15) 549-0858

I

North Star
Z80A. PROCESSOR BOARD ZPB-A

/

Contents
/

Cautions • . . . . . • • . . . . . . .
Introduction .
.........•
Limited Warranty . . . . • • • . . . . . .
Out of Warranty Repair . . . . . . . •
ZBP-A Parts List . • . . • . . . • . . . •
PROM Opt i on Parts List . . . . . . . . • .
A~sembly I n form~tion .
.. • .....
Figure lA: Component Identification
.
ZPBAssembly . . . .
•.•.•...•
ZBP Board Checkout .
..•..
..
PROM Option Assembly and Checkout
. .
Con f iguration Options
. .
The o ry of Operation
. . . . . . . . .
Append i x 1: Pulse Signal Detection . • . .
Appendix 2: S-100 Bus Signals . . . . • .
Assembly Figures .
. . • . . . . .
Schematic Drawings . . . . . •
. . ..
4

• • • • • • •

2
3
4
4
5
6
7
10
11
15
20
21
24
28
29
30
31

Copyright 1977, North Star Computers, I nc.
REVISION 2

CAUTIONS

1. Correct this document from the errata sheets, if any, before
doing anything else.
2. Building this product from a kit is a complex, demanding
project. It should not be attempted without prior kit
building experience.
3. Do NOT insert or remove the ZPB from the computer while the
power is turned on. Note that the power is not completely off
until the capacitors have discharged, several seconds after
turning of the power switch.
.
4. Do NOT insert or remove IC's from the board while the power is
turned on.
5. Be sure each 5 volt regulator is generating 5 volt output
voltage before installing any IC's.
6. Be careful to insert all IC's in correct positions and with
correct orientation. Be sure all IC pins are correctly
inserted into the socket holes and are not bent under the IC
and are not outside the socket.
7. Carefully observe the anti-static handling procedure for the
static sensitive devices (these are the Z80A and the 2708 PROM
in the PROM option). The procedure is described in the
Assembly Information section of this manual.

North Star Z80A PROCESSOR BOARD

2

INTRODUCTION

The North Star Computers Z80A Processor Board (ZPB) provides Z80
microprocessor capability on the S-100 bus. The use of the Z80A
chip allows full speed 4MHz operation as a standard feature. The
ZPB can be used in any standard S-100 bus computer and will
operate in conjunction with nearly all other S-100 bus boards.
However, the ZPB has been specifically designed to integrate into.
the North Star Computers HORIZON computer system. In addition to
the Z80A microprocessor and support logic to interface to the
standard S-100 bus, the ZPB contains the following features and
options:
1. AUTO-JUMP feature that will cause an automatic jump to any
address at power-on or reset.
2. VECTORED INTERRUPTS. ZPB logic will respond to eight levels
of interrupt requests, determine the highest priority request
pending and generate the appropriate RST instruction. The
logic may be disabled to allow the function to be performed on
another board.
3. FRONT PANEL INTERFACE for direct connection to IMSAI and other
similar front panels.
40 ADDRESS MIRROR feature to simulate the input/output
characteristics of the 8080 mieroprocesso[. This feature
maintains compatibility with some S-100 bus peripheral boards.
Address mirroring may be disabled to allow use of the more
powerful Z80 protocol.
5. PROM OPTION. lK of 2708 type erasable PROM can be 'added to
the ZPB. This allows configuration of systems that requ1re
resident monitor and bootstrap programs.
If you have purchased the ZPB as a kit, firyt skim this entire
manual. Before beginning assembly, careful~y read the Assembly
Information section.
Whether you purchased the ZPB as a kit or assembled, read the
Configuration section before attempting to use the ZPB. Note
that a Z80 Technical Manual has been included to fully describe
the operation of the Z80A.

3

North Star Z80A PROCESSOR BOARD

LIMITED WARRANTY
North Star Computers, Inc. warrants the electrical and mechanical
parts and workmanship of this product to be free of defects for a
period of 90 days from date of purchase. If such defects occur,
North Star Computers, Inc. will repair the defect at no cost to
the purchaser. This warranty does not extend to defects
resulting from improper use or assembly by purchaser, nor does it
cover transportation to the factory. Also, the warranty is
invalid if all instructions included in the accompanying
documentation are not carefully followed. Should a unit returned
for warranty repair be deemed by North Star Computers, Inc. to be
defective due to purchaser's action, then a repair charge not to
exceed $30 without purchaser's consent will be assessed. ANY
UNIT OR PART RETURNED FOR WARRANTY REPAIR MUST BE ACCOMPANIED BY
A COpy OF THE ORIGINAL SALES RECEIPT. This warranty applies to
units located outside the United S~ates of America only if all
costs and arrangements for transportation of the product to and
from the factory are borne entirely by the customer. This
warranty is made in lieu of all other warranties, expressed or
implied, and is limited to the repair or replacement of the
product. No warranty, expressed or implied, is extended
concerning the completeness, correctness, or suitability of the
North Star equipment for any particular application. There are
no warranties which extend beyond those expressly stated herein.

OUT·OF WARRANTY REPAIR
If your unit is out of warranty and you are unsuccessful at
diagnosing or repairing the problem, out-of-warranty service may
be arranged with a local dealer or other experienced local
computer technician. Alternatively, any North Star products may
be shipped PREPAID to the North Star address with a clear written
description of the problem. Include as many details as possible
about the problem and about your system configuration. Your unit
will be returned, C.O.D., within 30 days after receipt by North
Star. Out-of-warranty repair service is billed at the rate of
$25.00 per hour. If you wish to place an upper limit on the
amount of time spent on your unit, mention this in the written
description.

North Star Z80A PROCESSOR BOARD

4

ZPB-A PARTS LIST
1
1

1
1
7

14
14
1

1
2
2
I
2

2
2

ZPB Manual
Z80 Technical Manual
ZPB printed circuit board, 5" x Ie"
40-pin IC socket
20-pin IC sockets
l6-pin IC sockets
14-pin IC sockets
16-pin DIP header
lN4l48 diode
5 volt regulators, 7805 or 340T-5
heat sinks, 6107B-14
crystal, 8MHz
6-32x3/B" machine screws
#6 lock washers
6-32 nuts

Integrated Circuits

3
2
1
2
J
1
1
1
2

74LS00
74LS02
74LS03
74LS04
74LS08
74LS14
74LS32
74LS74
74LS75

1
1
'J

..J

7
2
1
<

1
1

74LS132
74LS148
74LS175
74LS241
74LS257
7404
74367
8T97
Z80A

Resistors
1
1

2
11
I

4
1

100 ohm
(brown-black-brown)
330 ohm
(orange-orange-brown)
470 ohm
(yellow-violet-brown)
lK ohm
(brown-black~red)
10K ohm
(brown-black-orange)
lK ohm networks, Part No. l0-9-l-R1K
2.2K ohm network, Part No. 10-9-l-R2.2K

Capacitors
I
1

19
2

1 .
1

5

33pf
470pf
.047uf
6.8uf
39uf
100uf

dipped mica (may be marked "330J03")
dipped mica
ceramic disc
dipped tantalum
dipped tantalum
electrolytic

North Star Z80A PROCESSOR BOARD

PROM OPTION PARTS LIST

2
1
1
1
1
3
1
1
1
1
4

74LS136 IC
2708 EPROM
+12 volt regulator, 78L12
-5 volt regulator, 79L05
24-pin IC socket
14-pin IC sockets
14-pin DIP header
lK resistor (brown-black-red)
3.9K resistor (orange-white-red)
3.9K resistor network, Part No. 10-9-1-R3.9K
2.2uf dipped tantalum capacitors

North Star Z80A PROCESSOR BOARD

6

ASSEMBLY INFORMATION
Read completely through each section before beginning the first
instruction step of that section. Perform all operations in the
sequence indicated. Read each step entirely, including any notes
that accompany the step, before beginning to follow the step.
WORK AREA AND TOOLS
Start with a clean, well-lit and well-ventilated area to work.
The area should be large enough to accommodate the kit, tools,
parts and assembly instructions~ Suggested tools are:
screwdrivers, needle-nose pliers, diagonal cutters, soldering
iron, solder, and masking tape. A number of tests will require
using a YOM (ohmmeter-voltmeter), or VTVM. Also highly
desirable, but not necessary, are an IC inserter, a screw-holding
screwdriver, an oscilloscope or logic probe, and an extender
card.
[Note that if you do not have an oscilloscope or logic
probe, waveforms can be detected by one of the procedures
described in Appendix 1.]
SOLDERING TIPS
For best results use a 15 to 25 watt soldering iron or an iron
with a temperature controlled tip (approximately 700 degrees).
The tip should be no wider than the solder pads on the printed
circuit board. Use only a fine gauge rosin core solder (60/40 or
63/37). Do NOT use acid core solder as this can severely damage
a printed circuit board. When soldering, keep the soldering iron
tip on the pad just long enough for the solder to completely
flow. If the solder does not draw up the wire then more solder
is required. Do not use so much solder that it overflows the:
pad. i~ a solidified joint is not sn1ny, 1L may be a cold solder
joint and should be remelted. The soldering iron tip should be
cleaned frequently by wiping on a damp sponge
When you have completed assembly of a board, inspect it for
unintended solder connections or "bridges", as well as unsoldered
leads. After soldering, it is recommended that the rosin flux be
removed from the board using flux remover, FREON or paint-thinner
type solvent. This will make looking for soldering problems
easier and give the board a clean, professional appearance.
IC SOCKET INSTALLATION
Integrated circuit (IC) sockets can be installed by first
inserting them into the printed circuit board, then placing
another flat board over the IC sockets and finally' turning over
this sandwich. Be sure that each IC socket is inserted into the
proper location and is oriented such that pin 1 of the socket
corresponds to the pin 1 indication on the PC board layout
legend.
(Refer to figure IA to identify pin I on an IC socket.)
To solder IC sockets, first solder just two opposite corner pins
7

North Star Z80A PROCESSOR BOARD

for all sockets being installed. Then remelt the corner
connections while applying pressure down on the board. This will
remove any gaps 'that may be present between the IC sockets and
the PC board. Finally, solder the remaining pins of the IC
sockets.
DIP HEADER SOLDERING
When making jumper connections on a DIP header, solder resistor
or capacitor lead snippings between the leads to be connected.
When more than two pins are to be connected together, bend a
sIngle wire so that it routes to each pin, and solder each pin
once. Insert the header in an IC socket on a PC board to hold it
during soldering. Overheating the pins with t~e soldering iron
will melt the plastic of the header. If there are multiple
jumpers on a header, make sure that no unintended connections are
made by carefully routing the jumpers, or by insulating each
jumper with some wire insulation.
RESISTOR AND CAPACITOR INSTALLATION
To install resistors or capacitors, first make right angle bends
in the leads to fit the PC board hole spacing.
(Some capacitor
leads are already appropriately spaced and do not need bending.)
Then insert the leads as far as possible through the correct
.
holes in the PC board and spread the leads slightly on the solder
side of the board to keep the part in place. After a grou~ of
resistors or capacitors has been inserted, then solder the leadS
on the solder side of the board and snip off the excess leads as
close to the board as possible. Use caution to avoid eye injury
from flying bits of wire. Save the lead clippings for later use
in making jumper connections.
PRINTED CIRCUIT BOARD LAYOUT
The white component layout legend is printed on the component
side of a printed circuit (PC) boar~. All components are
inserted from this side (component side) and soldered on the
other side (solder side). Locations on the PC board are
identified by two-character codes as marked on the board: a digit
followed by a letter indicating the horizontal and vertical
coordinates of the location. Note that in North Star kits, IC's
can be found on styrene pads in positions corresponding to their
intended locations on the PC board.
Pin nrimbering conventions for the S-l~~ edge pins are as follows:'
When viewing the component side of the board (with the pin edge
facing down), pins 1,2, ••• , 5~ range from left to right. When
viewing the solder side of the board, pins l~~, 99, ••• , 51 range
from left to right.

North Star

Z8~A

PROCESSOR BOARD

8

MaS INTEGRATED CIRCUIT HANDLING
Some North Star PC boards use some MaS-type IC's. These parts
are identified as such in the instructions. MaS devices can be
damaged by static electricity discharge, so special handling is
necessary to protect them. Handle MaS devices as little as
possible and avoid touching the pins. Place the conductive foam
or tube which contains the MaS device onto the PC board before
removing the device from the foam or tube. Also, be sure both
hands are touching the foam or tube when the device is removed
from the foam or tube.
Once a MaS device has been installed in a PC board, handle the
.board as little as possible. Of course, never insert or remove
any IC while power is applied to the board, and never remove or
insert a PC board while power is applied to the motherboard.

9

North Star Z80A PROCESSOR BOARD

c::=======~~
positive (+) lead \};...

100 MFD

)J::=======:3

.

Axial Lead
Electrolytic Capacitor

Resistor Network

========(€]DDD[:)~======~
Resistor

Ii'

-

Transistor and
Regulator (To-92)

positive
(+) lead
Quick-Connect
Lug

Integrated Circuit (lC)

Ceramic
Disc
Capacitor·

Dipped
Mylar
Capacitor

Dipped

Mica
Capacitor

I C Socket

Figure 1A. Identification and orientation of components.

Dipped
Tantalum
Capacitor

DIP Header

ZPB ASSEMBLY
Before beginning assembly of the ZPB, first check that you have
all the parts listed in the parts list.
Note tha t in the f01lowing instructions, "le ft" and "r ight" refer
to those directions when viewing the component side of the PC
board with the 100-pin edge facing down.
Using an ohmmeter, check for open circuits between the pair
of solder pads for each of the following seven capacitor
locations: C22, C23, C25,C26, C27, C28, and C29.
If any
shorts are found, locat~ and correct the problem or return
the PC board for repla'cement.
Insert and solder the 40-pin IC socket at location 3C,
following the procedure given in the Assembly Information
section.
Insert and solder the seven 20-pin IC sockets with correct
orientation.
Insert and solder a 16-pin IC socket at location IG.
Note
that this socket has reverse orientation from all the
others, with pin I in the upper right corner.
ZS.
t';;"2\

~

Insert and solder the remaining thirteen 16-pin sockets with
correct orientation.
Insert and solder the fourteen 14-pin sockets with correct
orientation.
Do not install sockets in locations 5C, 5D,
and 5E (inside dashed line) unless you are assembling the
PROM option at this time.
Insert and solder the five single-in-line (SIP) resistor
networks labeled RNI, RN2, RN4, RN5, and RN6 on the layout
legend.
RN6 is a 2.2K ohm network and the remaining four
are IK ohm networks.
RN3 is part of the PROM option.
Orient each SIP so the end marked with a "I" (sometimes this
end has a beveled corner) corresponds to the end marked with
a dot on the layout legend.

zs.

11

Insert and solder the following sixteen resistors.
Refer to
the Assembly Information section for resistor installation
procedures.
Resistor

Value

Color-code

Location

(~

470 ohm

yellow-violet-brown

IF

Rl

North Star Z80A PROCESSOR BOARD

~~

R2
R3
(V'j RS
(~ R6
(
R7
(v) R8

(~R9

(1
(Vr
(.

RII
Rl2
R13.
(~ Rl4
(
RIS
(v) Rl6
Rl7
(v R18

(V(
~
/ZrD

470
IK
IK
IK
330
IK
IK
IK
IK
lK
IK
lK
10K
100
lK

ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm
ohm

yellow-violet-brown
brown-black-red
brown~black-red

brown-black-red
orange-orange-brown
brown-black-red
brown-black-red
brown-black-red
brown-black-red
brown-black-red
brown-black-red
brown-black-red
brown-black-orange
brown-black-brown
brown-black-red

IF
2E
SG4F
4C
6B
6B
4G
7C·
7A
7A
8F
8G
8G
8G

Insert and solder the lN4l48 diode at location 8G. The end
of the diode marked with a band is the cathode end and
should be oriented toward the top of the board.
Insert and solder the l0flh:lf. electrolytic cap~cito.r (C29)
The posltlve end (marked wlth a "+" or a
red dot) should be oriented toward the right as indicated on
the layout legend. Some capacitors mark the negative end
with a "-" instead of the positive end.

~ located near 8A.

I

.

~.l. Insert and solder the 39uf tantalum capacitor (C2l) near
~ location 7G. Be sure to orient the capacitor so that the
lead marked with a "+" is inserted through the hole marked
with a "+".
~. Insert and solder the two 6.8uf tantalum capacitors (C22 and

~C23) at locations 8F and 8G.

Be sure to orient the
'capacitors so that the lead marked with a "+" is inserted
through the hole marked with~a "+".

G.l:V

Insert and solder the 470pf dipped mica capacitor (Cl) at
location IF. Some 470pf capacitors are marked "47lJO".

@~Inser~ and solder the 33pf dil?ped' mica capacitor (CS) at
. locatlon 2F.

Some 33pf capacltors are marked "330J03".

::. ~,O ' -V
Z19. with the computer power off, plug the partially assembled
board into the motherboard. Then turn on the power. with a
DC volt meter check that both regulators are generating 5
volts output. These voltages can be measured across the
pins of C22 and C23. wait a few minutes and measure again.
The regulators should not get very hot in this
configuration~
However, with all parts installed it is
normal for the regulator to feel quite hot to the touch.
Remember to turn off the power before removing the board.

e

Construct a 16-pin DIP header with jumpers set up for a
starting address of EB00 hex. This is the standard HORIZON
starting address. If some other starting address is
desired, change the header after completing the checkout
instructions. See figure lZ for the details of the header
configuration. Refer to the Assembly Information section
for header construction procedures. Plug the completed
header into location 2E (the POJ ADDRESS socket) with the
correct orientation. /
---,,!>"""t- 2. ...5, DCj
G '1,.. ~ -;. .) I 00
Insert the 33 integrated circuits (all exce?t the z80A
chip). Be sure that all IC's have pin 1 oriented to the
bottom left corner. Do not insert any IC's inside the area
for the PROM option (outlined with a dashed line).
SVO /J'YltV TOT
fJJ!O -z..-1?O!
Recheck the regulator output voltages as in step Zl9.

r

13

North Star Z80A PROCESSOR BOARD

Z23 •. Remove the PC board from the computer and then plug in the
Z80A chip with correct orientation. Refer to the Assembly
Information section for MOS device handling procedures.
Z24. Inspect the board in a good light to insure that:
A. all solder joints are good, i.e. there are no bridges of
solder beween adjacent solder joints, no unsoldered
joints, and no cold solder joints indicated by a dull
finish on the solder.
B. all IC pins are in the IC socket holes, not outside the
socket and not folded under the chip. Pins folded under
can often be detected by sighting down. a row of chips to
see if there is any blockage of light under the chips.
C. all parts are installed in the correct locations with the
correct orientation.
The ZPB is now completely assembled.
Checkout section.

Proceed to the RAM Board

North Star Z80A PROCESSOR BOARD

14

RAM BOARD CHECKOUT
The following checkout procedure should be followed for a newly
assembled board. It can also be used to diagnose problems in
previously operational boards.
This checkout procedure assumes that no other board besides the
ZPB is plugged into the S-100 bus. This makes it possible to get
the ZPB operational even if no other board in the system is yet
working. This procedure assumes only that the correct
unregulated voltages have been applied to the bus, that the
computer has a reset switch, and that the bus lines are not
shorted to each other.
The following terms are used in specifying expected test results.
GND
LOW
HIGH
+5V
AC

ground, 0 volts DC
logic zero, 0-.7 volts, normally about .3 volts
logic one, 2.4-5.0 volts, normally about 3 volts
+5 volts from power supply
Signal with pulses (as opposed to DC signal)

When referring to the name of a signal from the schematic
drawings, if the signal is identified with a bar over its name
then the name of the signal is followed by a slash (e.g., STORE/)
in the checkout instructions. When describing an AC pulse, the
notation (±W,P) refers to a positive or negative pulse with a
width of Wand a period of P. For example, a positive pulse of
width 125 nanoseconds appearing every 25 microseconds would be
represented as (+125ns,25us). See Appendix 1 for details on how
to detect pulse signals.
The abbreviation MB before a pin number indicates a bus pin on
the motherboard.
If an oscilloscope will be used to test the board, a "scope
ground" may be installed by soldering a "bridge" of jumper wire
between the two PC board holes that connect edge connector pins
50 and 100 near location 2A. Note that either of the two
regulator machine screws can also be used for ground test points.

~

Check for correct clock signals on the ZPB as follows:

A. Install a jumper wire at PE (near location 4G) if the PE
trace was has been cut.
B. Remove the lW jumper (near location 6G) if it was previously
installed.
15

North Star Z80A PROCESSOR BOARD

c •. Install a jumper wire at MW (near location 6A) if the MW
trace has been cut.
D. with the computer power off, install only the ZPB in the
computer motherboard.
E. Turn on the compu~er power and check for the following
signals. Note that'all timing signals~iven below assume
the ZPB is configuredfRr standard 4MHz operation.
",

Signal
v-PHI
VPHI 2
V;;HI 1
\ 2MH Z CLOCK/

Location

Description

Z80 pin 6
MB pin 24
MB pin 25
MB pin 49

AC,
AC,
AC,
AC,

t :fl~)

~ I-\.v,n-

{ qq'1 'bt-t

(+125ns,250ns) ......
(+ 125ns, 25 0ns')
C1v~
(+62ns,250ns)
W
\
\
q"1
(-250ns,500ns)
~"

If any of these are wrong, trace back to the crystal to
determine the cause.
This step will check the reset logic. Use the same setup as
the previous step and check the following signals while
alternately depressing and releasing the computer reset
switch.
Signal
RESET/
RST/
POC/

(91.

Location
I/MB pin
V7G pin
y'5G pin
","'MB pin

75
6
6
99

Switch
Depressed

Switch
Released

LOW
HIGH
LOW
LOW

HIGH
LOW
HIGH
HIGH

Check the auto-jump logic as follows:

A. Leave the board configured as in the previous step.
B. Turn off the computer power and remove the ZPB from the
computer. Temporarily connect the PRDY signal to ground by
soldering a piece of jumper wire beween 7F pin 5 and 7F pin
7 on the solder side of the ZPB.
C. Install only the ZPB in the computer 'motherboard and then
turn on the power and depress and release the reset switch.
The processor should pause immediately after performing the
auto-jump sequence and just before executing the first
instruction at the auto-jump address. Sheck that the SMI
signal at motherboard pin 44 is HIGH.~
D. Assuming the jump address specified on the header at
location E2 is E800, then E800 should be on the motherboard
address lines. HIGH signals should be observed on the
following, motherboard pins:
North Star Z80A PROCESSOR BOARD

16

./
pins 32,../ 85,/ '86,
and 87.V

LOW signals should be observed on the following motherboard
pins:
v v V'" Vv" v' v V ' / "/'
.
pins 29, 30, 31, 33, 34, 37, 79, 80, 81, 83, and 84

I

The processor should· have executed a single instruction (JMP
E800) and then gone into a wait state during the instruction
fetch at that address. The Theory of Operation section
describes the auto-jump sequence. If SMI is high but the
address is wrong, check the data paths through the POJ
header and multiplexors. If SMI is LOW, skip to the next
step to see if the processor can execute instructions at
all. If SMI has an AC signal, check the wait logic from
PRDY to WAIT/.
C4.

This step checks out the Z80A while executing a one
instruction program.

A. With the power off, remove the jumper from PRDY to ground
from the ZPB.
B. Turn on the power and then depress and release the reset
switch. The Z80 should be executing an RST 7 instruction
repeatedly. Observe that all the data input (01) lines are
HIGH by checking the following motherboard pins:

.

t/./

/

~..

~(if

/

plns 41, 42, 43,91, 93, 94, and 95

C. If you have an oscilloscope, then check that the signals
ZD0-ZD7 are HIGH during Ml at the Z80A chip pins:
/

pins 14, 15, 12, 8, 7, 9, 10, and 13 ~0 ~!.-'-.
D. Check that the following motherboard address lines are AC
signals:
v'
t/
V
pins 29-34, 37, and 79-87.
E. The RST 7 instruction causes a subroutine call to location
0038 hex, thus the stack address stored will be 0039 hex
(stored as alternating 00 byte and 39 hex byte). Thus,
observing the data output bus (DO), the following
motherboard bus pins should always be LOW:
pins 35, 40, 88, and 90. ~! \ Du,utcJ (,... tZ(;r~,)E::~:-;':
and the following motherboard bus pins should have AC
signals:
pins 36, 38, 39, and 89

17

North Star Z80A PROCESSOR BOARD

September 9, 1978

North Star Computers, Inc.
2547 Ninth Street
Berkeley, California 94710
Gentlemen:
I am resonding to your request for information regarding
possible errors in the Horizon documentation. I'm sure
it's redundant but here goes anyway:
ZPB-A board checkout procedure, page 17, par.
C4-E is no longer valid due to the addition of the
DO bus pull-up, RN6. These lines wi.ll go hi.gh
when ever the DO-EN line disables IC's 1 Band
1A giving an AC indication during the test.
Incidently, my Horizon I kit webt together beautifully
and so far, seems to be working like a champ!

//f)
L,)f

Check for the following signals at the Z80 chip:
Signal

Location

Description

PHI
Ml/
INT/
NMI/
WAIT/
RST/
Vcc
ground

pin
pin
pin
pin
pin
pin
pin
pin

AC, (+125ns,250ns)
AC, (-;,,500ns,2750ns)
HIGH ./
HIGH
HIGH
HIGH
+5V
GND

6
27
16
17
24
26
11
29

~The following signals should be observed .on the motherboard
bus lines:
Signal

Location

Description

XRDY

pin
pin
pin
pin
pin
pin
pin
pin
pin
pin
pin

HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
LOW
HIGH
AC, (+500ns,2750ns)
LOW

VI0/
VII/
VI2/
VI3/
VI4/
VI5/
VI6/
VI7/
NMI/
STAT-DSBL/
CC-DSBL/
ADDR-DSBL/
DO-DSBL/
PHLDA
PWAIT
PINTE
SMI
SOUT
SINP
SMEMR
SHLTA
SSW-DSBL/
PMREQ/
PRFSH/
MWRITE
RUN
PINT/
PHOLD/
PSYNC
PWR/
PDBIN
SWO/

3
~.

§

6
~

8
,9
3.13

.11
,12
. ·18
'
Pln
19
pin ,22
pin.·23
pin .:26
pin~ 27
pin 28
pin 44
pin-45
pin 46
pin- 47
pin .48
pin r53
pin 65
pin 6..6
pin 6j3
pin"7l
pin-73
pin~ 74
pin 76
pin 17
pin 78
pin 97
t

LOW

AC, (+375ns,2750.ns)
LOW
HIGH
AC, 4-pulses every 2750ns
AC, (-475ns,2750ns)
AC, (+250ns twice,2750ns)
HIGH
HIGH
HIGH
AC, 3 +pulses every 275f3ns
AC, (-250ns twice, 2750ns)
Z\C, (+360ns,2750ns)
A~, (-250ns twice, 2750ns)

North Star Z80A PROCESSOR BOARD

18

If these checkout steps have been successful, then the ZPB has
successfully done an auto-jump and executed a simple program.
Therefore, most of the circuits on the ZPB have been tested. The
ZPB should now have its configuration options set. Be sure to
remove all special jumpers added during the checkout. It is then
ready to be used in conjunction with the other boards in the
computer system. If the PROM option is being used, install it at
this time.
Diagnosis of a· problem in a previously operational board will
usually be successful using the following procedure:
1. Determine that the ZPB is in fact the board that has the
problem by attempting to use it in another computer.
2. Check that the regulator outputs are correct. Then, in an
orderly fashion begin replacing IC's in the ZPB with known
good parts until the problem disappears. If a board that was
working has not been subjected to any abnormal abuse then an
IC failure will be the cause of the problem in nearly every
case.
3. If the board is still failing then the problem may be a result
of any of the following less likely conditions: dirty edge
connector contacts, bad parts other than the IC's, bad
connection in an IC socket, or introduction of a short or open
in the traces on the board.

19

NorthStar Z80A PROCESSOR BOARD

PROM OPTION ASSEMBLY AND CHECKOUT

Before assembling the PROM option, the rest of the ZPB should be
completely assembled and checked-out.
Pl.

Insert and solder the 24-pin IC socket at location 4E with
the correct orientation.

P2.

Insert and solder the three 14-pin IC sockets with correct
orientation.

P3.

Insert and solder the resistor network RN3 at location 40 so
that pin 1 (or the beveled corner) corresponds to the dot on
the layout legend.

P4.

Insert and solder R4 (3.9K, orange-white-red) at location 3E
and R10 (lK, brown-blak-red) at location 5C.

P5.

Insert and solder the +12 volt regulator (~arked ~78L12~) at
location 01 (near location 8B). Also insert and solder the
-5 volt regulator (marked "79L05") at locatibn 02 (near
location 8B). The regulators should be oriented so that the
flat sides of the parts face the direction indicated on the
layout legend.

P6.

Insert and solder the four 2.2uf tantalum capacitors (C25,
C26, C27, and C28) at location 8B oriented so that the leads
marked with a "+" correspond to the holes marked with a .,+"
on the layout legend.

P7.

Using the 14-pin DIP header and some lead snippings
construct a header to determine the PROM location in memory.
Refer to the Configuration section (step J8) for details.
Plug the completed header into location 5E with correct
orientation.

P8.

Enable the PROM option by cutting the "PE" trace between
locations 3G and 4G.

P9.

Insert the 3 integrated circuits as indicated on the layout
legend with correct orientation. When inserting the PROM
observe the MOS device handling precautions given in the
Assembly Information section.

P10. The PROM option can now be checked out by reading the
contents of the PROM using a monitor program or control
panel. Note, however, that control panels which display the
01 bus (e.g., Altair) will not display the PROM contents.

North Star Z80A PROCESSOR BOARD

20

CONFIGURATION OPTIONS
There are a number of configuration options possible on the ZPB
that are specified by wIrIng jumpers on the board. The desired
configuration should be wired according to the following
instructions before the board is used.
Jl.

Signal grounding. Backplane pins 20 and 70 may be optionally
connected to ground. These connections can be made by
installing the jumpers labeled "EC20/1 and "EC70/1,
respectively, located at 6A. These connections should be
made unless these grounds would interfere with the operation
of other boards on the bus. Grounding these pins will
reduce backplane noise and thus provide more reliable
performance. Both pins should be grounded with a HORIZON.
Pin 20 should not be grounded for use with the IMSAI.
Neither pin should be grounded on an Altair.

J2.

Memory wait states. The "lW" jumper to the right of location
7G, if connected, forces at least one wait state on every
memory or I/O reference made by the processor.
(If a memory
board specifies one or more wait states, then that number of
wait states will be used for references to that board.) The
jumper should be installed if memory in the system is not
fast enough to run with zero wait states at 4MHz (about
300ns or faster) and the memory' itself cannot be configured
to have one wait state. If you are not sure your memories
are this fast, connect the jumper to get the system running
and experiment later. The North Star 16K RAM Board does not
require any wait states.

J3.

Processor speed. Normally the processor runs at 4MHz.
However, provision has been made to run at 2MHz. To achieve
2MHz operation, replace the 8MHz crystal at location IF with
a 4MHz crystal (not supplied). Then cut the "4" trace above
location 6F and install the "2" jumper instead. This keeps
the clock on backplane pin 49 at 2MHz as required by some S11313 bus boards.

J4.

Address mirroring. As required by some S-100 bus boards, the
ZPB simulates an 8080 during IN and OUT instructions by
driving the port address onto both 8-bit halves of the
address bus. To disable this feature and take advantage of
the greater flexiblility of the Z80, cut the "AM" (address
mirror) trace to the left of location 7F and install the
"NM" (no mirror) jumper instead.

J5.

Control panel. The ZPB normally generates the MWRITE signal
to backplane pin 68. If the ZPB is used in systems with
control panels or other boards that generate MWRITE, then
the "MW/I trace below location 6B should be cut. Leave the
trace in place for use in the HORIZON. Cut the trace when
used with an Altair or IMSAI.

21

North Star Z80A PROCESSOR BOARD

J6 • . Vectored interrupts. The ZPB is supplied with logic to
respond to an interrupt request on the vectored interrupt
request liries VI0-VI7 by generating the indicated RST
instruction. This logic may be disabled by installing the
"ID" jumper above location 7E. This will allow some other
board to respond to interrupt conditions.
J7.

PROM option. If the PROM option is installed, then the "PE"
trace to the left of 16cation 3G must be cut to en~ble the
on-board PROM.

J8.

PROM Address Selection. The lK bytes of on-board PROM can
be selected to reside in any of sixty-four lK regions of the
Z80 address space. The address selection logic compares the
six high order address bits (A10-A15) from' the Z80 against
the six bits specified with jumper wires on the header at
location 5E. Pins 8-13 correspond to the six address bits
A10-A15, respectively. All bits that should match a "zero"
bit should have their corresponding pins connected to pin 1
or pin 2 with jumper wires. All bits that should match a
"one" bit should have their corresponding pins connected to
pin 6 or pin 7 with jumper wires. Figure IP shows the
jumper pin assignments and some examples.

J9.

Auto-Jump Address Selection. Any of the 64K different
addresses may be specified as the auto-jump address with
jumper wires on the 16 pin header at location 2E. The eight
pins 9-16 on the header correspond to pairs of address bits
according to the following table.
Pin
9
10
11
12
13
14
15
16

Low Addr Bit
0
1
2
3
4
5
6
7

High Addr Bit
8
9
10
11
12
13
14
15

The address bit pins 9-16 should each be connected to one of
the pins 1-8 according to the following table:
Connect to pin 1 or 2 if both the high nrder and low
order address bits of the pair are "ones".
Connect to pin 3 or 4 if the high order address bit is a
"one" and the low order address bit is a "zero".
Connect to pin 5 or 6 if the high order address bit is a
"zero" and the low order address bit is a "one".

North Star Z80A PROCESSOR BOARD

22

Connect to pin 7 or 8 if both the high order and low
order address bits of the pair are "zeros".
For example, if bit 9 of the jump address is a "one" and bit
1 is a "zero" then pin 10 should be connected to pin 3 or
pin 4.
If jump address bit 15 is a "zero" and bit 7 is a
"zero" then pin 16 should be connected to pin 7 or pin 8.
Figure lZ shows the jumper pin assignments and some
examples.

23

North Star Z80A PROCESSOR BOARD

THEORY OF OPERATION

Z80A AND CONTROL CIRCUITS
The primary function of the ZPB is to interface the Z80A
processor to the S-100 bus with its control lines. The following
'list gives the S-L00 control signals along with pertinent
comments about their use and derivation. A slaah at the end of a
name indicates that the signal is active low (negative logic).
Pin Signal
22
19
23
68

78

26

74
73
28

65

12
99
72

Description

ADDR-DSBL/ Disables the address line drivers onto the S-100
bus when true.
Disables drivers for PSYNC, PDBIN, PWAIT, PWR,
CC-DSBL/
PMREQ, and PRFSH when true.
Disables
the data output bus (DO) drivers when
DO-DSBL/
true.
,
True during a memory write operation of the Z80.
MWRITE
This signal should be disconnected if the ZPB is
used in a system where MWRITE is generated on the
control panel board or some other.board.
PDBIN
Indicates. that the Z80 is reading the DI-;-:'bus
during a memory read, input, or interrupt
ackno~ledge operation4
The hold acknowledge response by the Z80 to a hold
PHLDA
req~est (PHOLD).
Indicates that the Z80 execution
is suspended and that a DMA bus operation may
begin.
Used to request the Z80 to sus.pend activity and
PHOLD/
allow direct memory access by a peripheral d'evice.
Interrupt request line to the Z80 from the onPINT!
board vectored interrupt logic or from some other
board.
This
signal ("interrupts enabled" on 8080 systems)
PINTE/
is normally true tiut goes false momentarily during
interrupt acknowledge sequences thus providing an
edge to latch the VI lines for boards such as the
IMSAI PIC-8.
PMREQ/
Memory cycle request signal from the Z80.
PNMI
Non-maskable interrupt request to Z80.
System reset synchronized to the Z80 clock. True
POC/
when the RESET switch is depressed or momentarily
when power first comes on.
When false, causes the Z80 to WAIT. Usually
PRDY
generated by memory boards to' extend memory cycles
for slow access time memories. See 'also XRDY.
North Star Z80A PROCESSOR BOARD

24

75
66

PRESET/
PRFSH/

76

PSYNC

27

PWAIT

77

PWR/

71

RUN

48
46
96
47
44

SHLTA
SINP
SINTA
SMEMR
SMI

45
21

SOUT
SS

98

SSTACK

53

SSW-DSBL

18

STA-DSBL/

97

SWO

03

XRDY

connected to the reset switch.
Dynamic memory refresh signal generated by the
Z80.
This signal is true between memory and/or IO
cycles of the Z80. Usually one clock cycle wide
(sometimes two). Usually used by wait state
counters on memory boards.
True when the Z80 is in the wait state caused by
PRDY or XRDY.
Timing" sign~l generated during memory write and
output operations which indicates that valid data
is on the DO bus.
Signal generated by a control panel to indicate
the processor should be in run mode
True if theZ80 is executing a halt instruction.
True during an input operation.
True during an interrupt qcknowledge operation.
True during a memory read operation~
True during the i~struGtion opcode fetch portion
of each instruction cycle of the Z80. For
instructions with two opcode bytes, this signal is
true twi~e.
,_;.~.
True durlpg output operatlons.
Generated by a control panel to indicate that the
Z80 should be in run mode during a single step
operation.
Always false. On 8080 systems indicates that a
stack reference cycle is in progress.
DisablesDI bus receivers and" enables CP bus
receivers. Used during input of sense "switches
from a control panel.
Disables drivers for SMEMR, SWO, SINP, SHLTA, SMl,
SOUT, and SINTA.
True when the Z80 is sending data out on the DO
bus.
Causes the Z80 to enter ~ait mode when false.
Usually generated by a control panel to cause a
control panel stop. There has been some conflict
of use between this signal and PRDY so care should
be taken to guarantee that drivers on this line
from different boards cannot be simultaneously
active.

DATA BUS
NOTE: This and the following sections will be more meaningful if
the schematic drawings are referenced while they are read. The
capitalized signal names refer to names used in the drawings.
The Z80 data bus (ZD0-ZD7) is the 8 data bits directly connected
to the Z80 processor. The data bus from the control panel (CP0CP7) is gated onto the ZD bus by the CPIN-EN signal during
control panel operations. The S-100 data input bus (DI0-DI7) is
25

North Star Z80A PROCESSOR BOARD

)

gated onto the ZD bus by the DI-EN signal during Z80 read
operations (RD-D) except on-board PROM reads and during interrupt
operations (XINTA). The ZD bus is gated onto the control panel
bus whenever a control panel operation is not in progress. The
ZD bus is gated onto the S-100 data output bus (D00-D07)' b'y DO-EN
during memory write and output operations of the Z80. The data
from the on-board PROM is gated onto the ZD bus directly by the
PROM-EN signal during on-board PROM read operations.
ADDRESS BUS
The sixteen address lines from the Z80 (ZA0-ZA15) are connected
through drivers to the S-100 address bus (A0-A15) except during
input/output operations.
In this latter case"if the address
mirroring feature is enabled then the low order 8 address bits
from the Z80 are gated onto both the top and bottom 8 blts of the
S~100 address bus.
This feature allows simulation of 8080 I/O
operations for systems that include S-100 boards that take
advantage of this 8080 characteristic •.
VECTORED INTERRUPTS
The on-board vectored interrupt capability provides for a
priority response to 8 interrupt levels. Whenever the Z80
generates an interrupt acknowledge condition (INTA), the state of
the eight interrupt request lines (VI0-VI7) is latched (8B, 8C)
and the latch outputs are fed to a priority encoder (8D). The
~hree encoder outputs indicate the highest priority pending
interrupt re~uest. These lines are merged with "1" bits at the
multiplexors (2D, IE) to provide the correct RST instruction on
the Z80 data bus (ZD0-ZD7) when the multiplexor is enabled by MXEN. The INT-RQ signal out of the encoder indicates that at least
,one interrupt request level is pending and causes an interrupt
request to the Z80 if on-board interrupts are enabled (OBIE).
AUTO-JUMP
The auto-jump feature causes an automatic jump to a jumper-wirespecified address (2E) upon power-on or reset. The register at
4G is configured to be a four state counter. The restart
condition (RST) resets the register and each successive read
cycle (RD) causes the register to shift to the next state until
the auto-jump sequence is done in the fourth state (AUJ-DONE).
The first three states cause the three bytes of an unconditional
jump instruction to the specified address to be multiplexed (IE,
2D) onto the Z80 data bus (ZD0-ZD7). The AUJ-DONE signal
disables the auto-jump feature until the next restart condition
reinitiates the entire sequence. The AUJS signal causes the two
address bytes to be selected by the multiplexors (IE, 2D) during
the second and third states. The jump opcode is generated during
the first state as a special case of the interrupt logic which
generates a JMP instruction rather than an RST.

North Star Z80A PROCESSOR BOARD

26

The auto-jump feature can be disabled by removing the 74LSl75
chip from location 4G.
ON-BOARD PROM OPTION
The ZPB has provision for one on-board 2708 type EPROM. The PROM
address can be specified by jumper wire selection (5E) to start
on any lK address boundary. The address comparison to test for
on-board PROM addresses is performed by the exclusive-or gates
(5C, 5D) The PROM is enabled (PROM-EN) if the high order 6
address bits compare during a memory read operation. A wait.
state is provided for the PROM so that the r~st of memory may run
at full speed.

27

North Star Z80A PROCESSOR BOARD

APPENDIX 1. PULSE SIGNAL DETECTION
Some steps in the checkout procedure will require test equipment
capable of distinguishing a signal containing pulses from a DC
signal. Anyone of the following will suffice.
1. Use of an oscilloscope is best since the shape and frequency
of the pulses can also be determined.
2. Use a logic probe that detects pulses.
3. If the ZPB is being assembled for use with a HORIZON, then use
a counter on the motherboard to divide the frequencies down to
the audio range and then play the result through a hi-fi
amplifier. To do this, remove the 74LS161 at location 7D on
the motherboard. Then attach the test probe wire to jumper 2D
pin 16 (this is the input to the divider). Next, take the
output of the divider at jumper 10A pin 11 and connect to the
AUX input of the audio amplifier. Finally, connect the AUX
input ground on the audio amplifier to signal ground on the
motherboard. This arrangement will divide high frequency
signals by 4096 and thus put the resulting signal in the
audible range. Thus a 4 MHz signal will be heard as a tone
one octave higher than a 2MHz signal.
4. Construct the "probe" shown in figure lC on a piece of
cardboard or perf-board. This probe converts high frequency
signals to DC signals. The voltage of the resulting DC signal
will be proportional to the duty factor of the tested wave
form.

North Star Z80A PROCESSOR BOARD

28

APPENDIX 2. S-100 BUS SIGNALS
PIN #
1

2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
3~

36
37
38
39
40
41
42
43
44
45
46
47
48
49
50

29

PIN #

SIGNAL
+8 VOLTS
+16 VOLTS
XRDY
VI0/
VII/
VI2/
VI3/
VI4/
VIS/
VI6/
VI7/

STA-DSBL/
CC-DSBL/
GROUND (optional)
SS
ADDR-DSBL/
DO-DSBL/
PHI 2
PHI 1
PHLDA
PWAIT
PINTE
AS,
A4
AJ:
AIS
A12
A9
001
00,0
A10
004
DOS
D06
012
013
017
SM1
SOUT
SINP
SMEMR
SHLTA
2MHZ CLOCK/
GROUND

I

51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100

SIGNAL
+8 VOLTS
-16 VOLTS
SSW-DSBL/
EXT-CLR/

GROUND (optional)

PMREQ/
PRFSH/
PHANTOM
MWRITE
PSI
GROUND (optional)
RUN
PRDY
PINT/
PHOLD/
PRESET/
PSYNC
PWR/
PDBIN
A0
Al
A2·
A6'
A7'
A8 .
A13
A14
All
~

DO"l...

D03
D07
DI4
DIS
DI6
DI1
010
SINTA
SWO
SSTACK
POC/
GROUND

North Star Z80A PROCESSOR BOARD

SOURCE OF ONES

SOLJRCf: OF

80TH BYTES

IN

ONES. IN

HI BYT E

~======jfr;:~

BIT 7
ilT
SIT
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BIT
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ZEROES IN LO BYTE 5

SOURCE OF ZEROES IN HI BYTE? "~=====::::J
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I

SOURC.E OF ZEROES IN BOTH BYTES

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North Star Z80A PROCESSOR BOARD

30

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