North Star RAM-16-A User manual

IskxttiSld^
N orH nS b iC om p u ters Inc.
2547 Ninth Street
Berkeley, Ca, 94710
North Star
16K Ram Board
Copyright® 1978, North Star Computers, Inc.
RAM-16-DOC
R e v is io n 2

North Star
16K RAM Board
Table of Contents
Introduction .... ..........................
Cautions . ....................... . .
Limited Warranty ................ . . . . . . .
Out of Warranty Repair . . . .... .........
RAM-16-A Parts List . .................... . . .
Parity Option Parts List .....................
Assembly Information .... .................
Figure 1A: Identification of Components . . .
RAM Board Assembly . ..........................
RAM Board Checkout . . . .
Parity Option Assembly and Checkout ........
Configuration . ..................... . . .
Using the Parity Option . . ....................
Using Bank Switching . . . . . . . ..... .
Theory of Operation ......... ...............
Special DMA Applications ......... ..
Appendix 1: Pulse Signal Detection ........ ..
Appendix 2: Memory Test Program .......
Appendix 3: Organization of RAM Chip Array . .
Schematic Drawings ..................... . . .
2
2
3
3
4
5
6
9
10
15
20
22
24
26
27
31
32
33
36
37

INTRODUCTION
The North Star 16K byte RAM board (RAM-16-A) is compatible with
S-100 computers. The board will operate at full speed with both
8080 and Z80 microcomputers, even with 4 MHz operation. The
industry standard 16-pin 4027 RAM chip (200 nanoseconds access)
is used. A parity option is available for use with the RAM-16-A.
The RAM-16-A may be addressed to any 16K region beginning at any
8K boundary. The RAM-16-A has a bank switching feature which
allows more than 64K bytes of RAM to be used in the computer, and
also facilitates special software applications such as time
sharing .
If you have purchased the RAM-16-A as a kit, then first skim the
entire manual. Be sure to carefully read the Assembly
Information section before beginning assembly. If you have
purchased the RAM-16-A in assembled form, you may skip the
Assembly section. Regardless of whether you purchased the RAM-
16-A as a kit or assembled, be sure to read the Configuration
section which discusses how to configure the RAM-16-A for each
individual application.
CAUTIONS
1. Correct this document from the errata sheets, if any, before
doing anything else.
2. Assembly of this product from a kit is a complex, demanding
project. It should not be attempted without previous kit
building experience.
3. Do NOT insert or remove any boards from the computer when the
power is on. Note that power is not completely off until the
capacitors have discharged, several seconds after turning off
the computer power switch.
4. Do NOT insert or remove IC's from any board while the power
is turned on.
5. Be sure that all IC's are inserted in their correct positions
and with correct orientation before turning on the power. Be
sure that all IC pins are correctly inserted in the socket
and are not bent under the IC and are not outside the socket.
6. Carefully observe the prescribed rules for handling the MOS
type integrated cirucits. The handling procedures are
described in the Assembly Information section of this manual.
North Star 16K RAM Board 2

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 limited 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 pröblem, 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.
3North Star 16K RAM BOARD

RAM-16-A PARTS LIST
1 RAM-16-A Manual
1 RAM-16-A printed circuit board, 5“ x 10"
2 20-pin IC sockets
39 16-oin IC sockets
21 14-pin IC sockets
1 14-pin DIP header
1 8-position DIP switch
1 delay line, DDU-4-7781 or STTLDM-400
1 +5 volt regulator, 7805 or 340T-5
1 +12 volt regulator, 7812 or 340T-12
1 -5 volt regulator, 79L05
1 heat sink, 6106B-14
1 heat sink, 6107B-14
2 6-32x3/8" machine screws
2 #6 lock washers
2 6-32 nuts
Integrated Circuits
274LS00 1 74LS373
1 74LS02 174LS393 (or 74393)
174LS08 1 7402
174LS13 1 74S00
274LS14 2 74S10
174LS30 1 74S30
1 74LS74 174S74
174LS75 1 74S113
174LS123 (or 74123) 1 74S138
274LSI32 1 74S175
1 74LS241 32 4-027-3 (MOS)
374LS352
Resistors
82.2K ohm 1/4W red-red-red
1220 ohm 1/4W red-red-brown
3330 ohm 1/4W orange-orange-brown
1 470 ohm 1/4W yellow-violet-brown
110K ohm 1/4W brown-black-orange
118K ohm 1/4W brown-qray-orange
822 ohm 1/4W red-red-black
14.7K ohm resistor network, 10-pin
North Star 16K RAM Board 4

Capacitors
2 .0047uF dipped mylar
133pF dipped mica (may be marked "330J03")
347pF ceramic disc
1 100pF dipped mica
56.8uF dipped tantalum
22.2 uF diooed tantalum
60 .047uF ceramic disc
PARITY OPTION PARTS LIST
1 74LS109 IC
2 74LS280 IC
1 75452 IC (8-pin)
4 4027-3 IC (MOS)
5 16-pin IC sockets
2 14-pin IC sockets
1 8-pin IC socket
1 220 ohm 1/4W resistor (red-red-brown)
1 LED
5North Star 16K RAM BOARD

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, ahd masking tape. A number of tests will require
using a VOM (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. If a solidified joint is not shiny, it 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 1A to identify pin 1 on an IC socket.)
To solder IC sockets, first solder just two opposite corner pins
North Star 16K RAM Board 6

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 the 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 group 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) board. 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 numbering conventions for the S-100 edge pins are as follows:
When viewing the component side of the board (with the pin edge
facing down), pins 1,2, .... 50 range from left to right. When
viewing the soider side of the board, pins 100, 99, ..., 51 range
from left to right.
North Star 16K RAM BOARD
7

MOS INTEGRATED CIRCUIT HANDLING
Some North Star PC boards use some MOS-type IC's. These parts
are identified as such in the instructions. MOS devices can be
damaged by static electricity discharge, so special handling is
necessary to protect them. Handle MOS devices as little as
possible and avoid touching the pins. Place the conductive foam
or tube which contains the MOS 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 an MOS 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.
North Star 16K RAM Board 8

€ B O
Resistor
Regulator (To-220)
Quick-Connect
Lug
Ceramic
Disc
Capacitor
Dipped
Mylar
Capacitor
Dipped
Mica
Capacitor
Dipped
Tantalum
Capacitor
Integrated Circuit (1C) 1C Socket D I P Header
9Figure 1 A. Identification and orientation of components.

RAM BOARD ASSEMBLY
Before beginning assembly of the RAM board, first check that you
have all the parts listed in the parts list. This manual applies
to the RAM-16-A3 board revision - check the PC board marking to
be sure you do not have a RAM-16-A2 board. Note that in the
following instructions, '‘left" and "right“ refer to those
directions when viewing the component side of the PC board with
the 100-pin connector facing down.
*/^Rl. Using an ohmmeter, check for open circuits between the pair
of solder pads for each of the following six capacitor
locations: Cl, C 2, C3 , C4, C5, and C6. If any shorts are
found, locate and correct the problem or return the PC board
for replacement.
R!2. Insert and solder the two 20-pin IC sockets at locations 8D
and 17E on the PC board. Follow the procedure described in
the Assembly Information section. Be sure the sockets are
installed with the correct orientation (all the IC's have
pin 1 toward the top of the board.
. /
yR3. Insert and solder the thirty-nine 16-pin sockets with
correct orientation. Do not install a socket at the switch
position (7A). Do not install any sockets in the positions
reserved for the parity option unless you will be assembling
the parity option at this time. The parity option sockets
/ are located at positions 3A, 9A, 9B, 9C, and 9D.
^R4.
V
R5
Insert and solder the twenty-one 14-pin sockets with correct
orientation. Do not install sockets at locations 10E or
15E, unless you are assembling the parity option at this
time.
Now check all the solder joints for possible solder bridges
between adjacent solder pads, unsoldered connections, or
cold solder joints.
Insert and solder the following resistors:
Resistor
a ri
M R3
( t / l R4
M / R5
(V) R6
( \ Ä R 7
(x>J R8
M R9
(J) R10
M Rll
M R13
Value Size Location Color-code
2.2K 1/4W 0A red-red-red
330 1/4W 2D org-org-brn
2.2K 1/4W 7A red-red-red
18K 1/4W 1A brn-ary-org
470 1/4W IB yel-vio-brn
10 K 1/4W 2A brn-blk-org
2.2K 1/4W 7A red-red-red
2.2K 1/4W 3D red-red-red
330 1/4W 10E org-org-brn
2.2K 1/4W 6A red-red-red
2.2K 1/4W 5C red-red-red
North Star 16K RAM Board 10

(e>-R14
{ J f R15
M R16
( V R17
(y) .R18
( -f, R19
(✓f R20
R21
(-4 R22
(fcf R23
M " R24
2.2K 1/4W 6C red-red-red
2.2K 1/4W IB red-red-red
22 1/4W - 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
22 1/4W 8B red-red-blk
330 1/4W 12E org-org-brn
Insert and solder the single-in-line (SIP) resistor network
labeled RN1 on the layout legend at location 16E. Orient
the 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.
Save the resistor R12 (220 ohm, red-red-brn) for future
special DMA applications. See the Special DMA Applications
section for details. Note that the other omitted resistor,
R2, is only installed with the parity option.
I/”
R8 Insert and solder the 8-position DIP switch at location 7A.
Orient the switch so that "ON’' is to the right. The DIP
switch solders directly to the board without a socket.
0R9. Install and solder the 5 volt 7805 regulator and 6106-14
heat sink (the larger of the two heat sinks) at location 04.
Neatly bend the regulator leads so they will route over the
edge of the heat sink and down through the holes in the PC
board without touching the heat sink or each other. Insert
the regulator leads into the PC board holes and then attach
the regulator and heat sink to the board with a 6-32x3/8"
machine screw so that the following order results from
bottom to top: machine screw head, PC board, heat sink,
regulator, lock washer and nut. Before tightening the
machine screw, position the heat sink regulator assembly as
far as possible from the edge of the PC board. Finally,
/solder the regulator leads.
/ '
[ \ ß i 0 . Install and solder the 12 volt 7812 regulator and 6107-14
heat sink at location Q3 . Follow the procedure of the
previous step.
/fell. Insert and solder the 79L05 regulator at location Q l ,
orienting the regulator so that the flat edge corresponds to
...the flat edge indicated on the layout legend.
.
U-R12. Insert and solder the following tantalum capacitors , being
careful to insert the + lead of each capacitor into the hole
marked " + •* on the layout legend. The + lead is sometimes
indicated by a red dot on the capacitor. Refer to the
North Star 16K RAM BOARD
11

Assembly Information section for capacitor installation
procedures.
Capacitor Value Location
(O Cl
L , r C2
( C3
(. ) C4
( ••) C5
(>•') C6
Cll
2.2uF 0A
2.2uF 0A
6.8uF 0B
6.8uF 0B
6.8uF 0D
6.8uF 0D
6.8uF 8A
R13. Insert and solder the following capacitors:
Capacitor Value Location Type
U T C l
( ,) C8
(I)'', C9
( v)/ Cl2
( C13
(«4 C14
. 0047uF 1A
10 0pF 1C
.0047uF 2A
47pF 2E
47pF 12E
47pF 12E
dipped mylar
dipped mica
dipped mylar
ceramic disk
ceramic disk
ceramic disk
■'K14. Insert and solder the sixty .047uF ceramic disk capacitors
at the 60 locations marked on the layout legend with
asterisks.
R15. Save the remaining 33pF capacitor (C10) for special DMA
applications. See the Special DMA Applications section for
/ details.
/'
.R16. Be sure the computer power is off and then insert the RAM-
' 16-A board into the computer motherboard. Now turn on the
power and check for the following voltages across each
indicated pair of capacitor leads:
Capacitor Voltage
( ) C5 +5V ±5%
( ) Cl +$2V-$f%
Turn off the computer power. If any of the voltages are not
correct, then locate and correct the problem before
proceeding.
R17. Install the delay line module in the socket at location 5A.
Orient the delay line so that pin 1 (indicated by a dot or
"'"“IN“) is inserted in pin 1 of the socket.
Install the 28 TTL integrated circuits (all but the memory
IC's). Be careful to orient each IC so that pin 1 is
North Star 16K RAM Board 12

inserted into pin 1 of the socket.
Location IC
( ) 1A 74LSI23 (or 74123)
( ) IB 74LSI3
( ) 1C 74LSI32
( ) ID 74LS14
( ) 2A 74S175
( ) 2B 74LS00
( ) 2C 74LS14
( ) 2D 74S74
( ) 3B 74LS08
( ) 3C 74LS132
( ) 3D 74LS352
( ) 4A 7402
( ) 4B 74S30
( ) 4C 74LS02
( ) 4D 74LS352
( ) 5B 74S113
( ) 5C 74LS393
( ) 5D 74LS352
( ) 6A 74S138
( ) 6B 74LS75
( ) 6C 74LS74
( ) 6D 74LS30
( ) 7B 74S00
{ ) 7C 74LS00
( ) 8A 74S10
( ) 8C 74S10
( ) 8D 74LS241
( ) 17E 74LS373
Carefully following the MOS device handling procedures
described in the Assembly Information section, install the
thirty-two 4027 memory IC's. Be careful to orient each
memory IC so that pin 1 is inserted into pin 1 of the
socket. Since the capacitors cause a tight fit, it is
easier to insert rows B and C before rows A and D.
. Inspect the PC board to see that all the IC pins are
properly inserted into the socket holes. Check that no pins
are bent under the IC, and that no pins are outside the
socket.
lrsx" R21 .• If you are assembling the RAM-16-A board for use with the
HORIZON computer, install the three “G" jumpers at locations
2E, 5E, and 6E by soldering with a piece of resistor
snipping. If you have a different computer, it is strongly
recommended that bus pins 20, 61, and 70 (if not used for
other purposes) be connected to ground on the motherboard so
that the "G“ jumpers may be used on the RAM-16-A board. If
all three jumpers cannot be used, use as many as possible.
13 North Star 16K RAM BOARD

Connecting these pins to ground will help reduce excessive
ground noise on some S-100 computers.
R22. Configure the 14-pin DIP header for location 7D as follows:
A. Connect pin 1 to pins 2 and 3.
B. Connect pin 6 to pin 7.
This configuration of the header is for use of the RAM-16-A
board with a Z80 or Z80A microprocessor in an application
where bank switching is not needed. For 8080 and/or bank
switching use, configure the header as described in the
Configuration and Using Bank Switching sections.
R23. If this board is to be used with a processor board which
sources POC/ (bus pin 99) as an indication that the
processor is being reset (e.g., North Star, Imsai, Vector
Graphics, Processor Technology) then skip this step. For
use with other processors (e.g. , Altair 8800), cut the trace
connecting 3C pin 5 with 3C pin 4 on the solder side of the
board, and add a jumper between PRESET/ (bus pin 75) and 3C
pin 4 on the component side of the board.
The assembly of the RAM-16-A board (less parity option) is now
complete. Proceed to the checkout section.
North Star 16K RAM 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.
The following terms are used in specifying expected test results:
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 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 W
appearing with a period of P. For example, a positive pulse with
width 120 nanoseconds appearing every 25 microseconds would be
described as (+120ns,25us). See Appendix 1 for details on how to
detect pulse signals.
If an oscilloscope will be used to test the board, a "scope
gound" may be installed by soldering a "bridge" of jumper wire
between two of the three PC board holes that connect edge
connector pins 50 and 100 near location 13E. Note that either of
the two regulator machine screws can also be used for ground test
points.
Cl. If your S-100 bus computer has a control panel, then check
out control panel operation of the RAM-16-A as described in
this step. Otherwise, skip to step C2.
A. Set the address select switches for the region where
the RAM-16-A will be used (refer to the Configuration
section for details).
B. With the computer power off, install the RAM-16-A board
into the motherboard.
C. Using the control panel, attempt to deposit the zero
value in the first byte of each 4K address region on
the board. Then examine these addresses. If the
values examined are not all zero, then skip to step C3.
Otherwise, continue at step C2.
C2. If you do not already have a working computer, then skip to
step C3. Otherwise, set the address select switches for an
available 16K address region (see the Configuration
section). Then, with the computer power off, install the
RAM-16-A board into the computer motherboard. Now use a
15 North Star 16K RAM BOARD
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)

memory test program to verify correct operation of the
board. If you do not have a memory test program (such as
the TM command in the North Star Monitor), then use the
program listed in Appendix 2.
If the RAM-16-A does not fail the memory test after several
hours of operation, then the board is operational and you
may skip the remaining checkout steps. If systematic data
or addressing errors are detected, then refer to the
schematic drawings to diagnose and correct the problem.
(The correspondence between addresses and RAM chips is given
in Appendix 3.) If the RAM-16-A does not operate at all,
then continue with step C3.
C3. Set the address switches labeled "2" and "3" on the DIP
switch (2nd and 3rd from the top) to the "ON" position. The
other six switches should be OFF. With the computer power
off, install ONLY the processor board and the RAM-16-A into
the computer motherboard. Turn on the power and depress and
hold down the computer reset switch so that no memory
requests are being made.
A. Check the following memory cycle request signals while the
computer reset switch is depressed:
Signal Location Description
STORE/
INSTRUCTION-FETCH/
FETCH/
RUNNING-REFRESH/
DEPOSIT-CY/
4B pin 5HIGH
4B Pin 11 HIGH
4B pin 6HIGH
6C pin 6 HIGH
4B pin 4 HIGH
If the signals are not as listed then refer to the schematic
drawings and trace backwards to locate and correct the
problem.
B. WAITING-REFRESH cycles should occur approximately every 25
microseconds. In the following table, let T refer to the
period of PHI 2 in your computer (e.g., 250ns with a 4MHz
processor and 500ns with a 2MHz processor). Check the
following signals while the computer reset switch is
depressed:
Signal Location Description
WRF
WAITING-REFRESH/
CYCLE-START
delay tap T1
delay tap T2
delay tap T3
delay tap T4
2A Pin 3AC, (+T i
,25us)
1C pin 12 AC, (-T i
,25us)
4B pin 8AC, (+T,
,25us)
5A pin 12 AC , ( +T,
,25us)
5A pin 4AC, (+T,
,25us)
5 A pin 10 AC, (+T,
,25us)
5A pin 6AC, (+T,
,25us)
North Star 16K RAM Board 16

delay tap T5
CYC-ENn/
RAS-A/
RAS-B/
RAS-C/
RAS-D/
chip address bit 0
chip address bit 1
chip address bit 2
chip address bit 3
chip address bit 4
chip address bit 5
Note: Sometimes
5A pin 8 A C,
8C pin
9A pin
9B pin
9C pin
9D pin
9A pin
9A pin
9A pin
9A pin
9A pin
9A pin
(+T,'25us)
(-T-135ns,25us)
(-T-40ns,25us)
(-T-40ns,25us)
(-T-40ns,25us)
(-T-40ns,25us)
see note
see note
see note
see note
see note
see note
(+T-90ns,25us)
(+T,25us)
6AC ,
4 AC,
4AC ,
4 AC,
4AC,
5 AC,
7AC,
6AC ,
12 AC,
11 AC,
10 AC,
and sometimes
If the signals are not as listed, then refer tg the
schematic drawings and trace backwards to locate and correct
the problem.
”se the same setup as step C3 . If the computer includes an
auto-jump capability, then it should be set to jump to some
address outside of the range 2000 hex through 5FFF hex (for
example, E800 hex or 0). If the processor board has- a PROM
option at address 0, it should be disabled for this step.
With the computer power on, depress and release the reset
switch. The processor should repeatedly execute RST 7
instructions (FF hex) from address 38 hex. This should
cause memory store requests to all addresses (resulting from
the RST instruction stack pushes). Check the following
signals:
Signal Location Descr iption
INSTRfTCTION-FETCH/ 4B pin ii AC, (-220ns,11T)
FETCH/ 4B Pin 6 AC, see note 1
STORE/ 4B pin 5 AC, (-220ns twice,11T)
RUNNING-REFESH/ 6C pin 6AC, (-260ns,11T)
RAS-A/ 9 A pin 4 AC, see note 2
RAS-B/ 9B pin 4 AC, see note 2
RAS-C/ 9C pin 4 AC, see note 2
RAS-D/ 9D Pin 4AC , see note 2
chip write enable 9A pin 3AC , (-220ns twice,11T)
CAS-A/ 9 A pin 15 AC , (-210ns thrice,11T)
CAS-B/ 9B pin 15 AC, (-210ns thrice,11T)
CAS-C/ 9C pin 15 AC, (-210ns thrice,11T)
CAS-D/ 9D pin 15 AC, (-210ns thrice,11T)
Note 1: (-100ns,11T) with Z80A, '(-210ns,11T) with 8080.
Note 2: Sometimes (-225ns,11T) and sometimes
(-225ns twice,11T).
If the signals are not as listed, refer to the schematic
North Star 16K RAM BOARD

drawings to locate and correct the problem.
C5. This step will test the memory fetch and store operations by
forcing the computer to execute alternating RST 7 and
MOV A,A instructions repeatedly.
A. Set the address select switches labeled "I" and "2" on the
nip switch (1st and 2nd from top) to the ON position. The
other six switches should be OFF.
B. With the power off, remove the 74LS373 IC from location 17E
of the RAM board. (This disconnects the RAM-16-A from the
DI bus.)
C. With a piece of jumper wire, make a temporary solder
connection between 17E pin 15 (DI7) and 5D pin 6 (A0) o‘n the
solder side of the RAM-16-A.
D. If the processor board has a PROM option, it should be
disabled for this step.
E. With the power off, install ONLY the processor board and the
RAM-16-A board in the computer motherboard.
F. Turn on the computer power. The repeated executions of the
RST 7 instruction should fill the entire RAM-16-A board with
alternating bytes containing 3A hex and 00 (resulting from
the stack pushes of the RST instruction).
G. Check the following signals at the memory chip at location
10D:
Signal Location Description
Vbb
DI
WE/
RAS/
A0/
A2/
Al/
Vdd
Vcc
10D pin 1 -5V
10D pin 2 mostly HIGH, LOW during first PWR
10D pin 3 AC, two pulses, one during each PWR
10D pin 4 AC, see note 1
10D pin 5 AC, see note 2
10D pin 6 AC, see note 2
10D pin 7 AC, see note 2
10D pin 8 +12V
10D pin 9 +5V
A5/
A4/
A3/
CS/
DO
CAS/
Vss
10D pin 14 AC, see note 3
10D pin 15 AC, see note 4
10D pin 16 0V
10D pin 10 AC, see note 2
10D pin 11 AC, see note 2
10D pin 12 AC, see note 2
10D pin 13 GND
Note 1: Usually four pulses per loop (15T or 16T), two at
Ml leading edges for fetches; two at Ml trailing edges
North Star 16K RAM Board 18

Note 2: Signal is complicated, with many transitions per
loop.
Note 3: Rises during one SMI pulse, falls during the
next, alternately. Additionally, for those stores that
actually reference the chip (1/16 of the stores), the
signal goes LOW during the first store and HIGH during
the second.
for refresh. Occasionally two more during stores.
Note 4: Four pulses per loop, two fetches and two stores.
H. Check the following data output signals on the RAM-16-A. If
you are using an oscilloscope, then trigger on ID pin 11 or
the upper end of R10 at 12E (SMI) on the RAM-16-A.
Signal Location
MD5 10. A pin 14
MD4 11A pin 14
MD6 12A pin 14
MDl 13A pin 14
MD0 14 A pin 14
MD2 15A pin 14
MD3 16A pin 14
MD7 17A pin 14
Description
AC, see note 3 above
AC, see note 3 above
see note 5 below
AC, see note 3 above
see not 5 below
see note 5 below
AC, see note 3 above
see note 5 below
Note 5: Mostly low, high during store cycles outside of
the address range of the board.
I. Replace the 74LS373 at location 17E, replace the 74LS280 at
location 10E if it was removed, remove the jumper wire, and
re-enable the processor board PROM option if it was
disabled.
19 North Star 16K RAM BOARD