Richard Cini
10 years ago
All â¹
Not sure if this may be related to the problems we¹re seeing with this
board, but I was looking at my CompuPro backplane and I noticed that pins 20
and 70 are grounded per the IEEE696 specification, while on the IMSAI, only
pin 70 is grounded. Pin 20, I believe, is the UNPROT signal.
Maybe it¹s not the problem, but I think everyone should try isolating pin 20
from the bus by leaving both J3 and J4 open or otherwise confirming that pin
20 is not connected to ground at the bus. The only issue with this is if you
use an early memory card that requires a high on pin 20 to enable writing it
won¹t work. I remember having to isolate 20/70 on certain CompuPro cards in
order to get them to work with the IMSAI.
Just a thoughtÅ
Rich
--
Rich Cini
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator
http://www.classiccmp.org/cini
http://www.classiccmp.org/altair32
Not sure if this may be related to the problems we¹re seeing with this
board, but I was looking at my CompuPro backplane and I noticed that pins 20
and 70 are grounded per the IEEE696 specification, while on the IMSAI, only
pin 70 is grounded. Pin 20, I believe, is the UNPROT signal.
Maybe it¹s not the problem, but I think everyone should try isolating pin 20
from the bus by leaving both J3 and J4 open or otherwise confirming that pin
20 is not connected to ground at the bus. The only issue with this is if you
use an early memory card that requires a high on pin 20 to enable writing it
won¹t work. I remember having to isolate 20/70 on certain CompuPro cards in
order to get them to work with the IMSAI.
Just a thoughtÅ
Rich
--
Rich Cini
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator
http://www.classiccmp.org/cini
http://www.classiccmp.org/altair32
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