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drawings to locate and correct the problem.
CS.
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 "1" 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 IS (DI7) and SD pin 6 (A0) oh 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
10D pin 1
-SV
DI
10D pin 2
mostly HIGH, LOW during first PWR
WEI
10D pin 3
AC, two pulses, one during each PWR
RAS/
10D pin 4
AC, see note 1
A0/
10D pin S
AC, see note 2
A2/
10D pin 6
AC, see note 2
Al/
10D pin 7
AC, see note 2
Vdd
10D pin
8
+12V
vcc
10D pin
9
+SV
AS!
10D pin 10
AC, see note 2
A4/
10D pin 11
AC, see note 2
A3/
10D pin 12
AC, see note 2
CS/
10D pin 13
GND
DO
10D pin 14
AC, see note 3
CAS/
10D pin IS
AC, see note 4
vss
10D pin 16
0V
Note 1: Usually four pulses per loop (1ST or 16T) , two at
Ml leading edges for
fetches~
two at Ml trailing edges
North Star 16K RAM Board
18
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