IMSAI (moving along...)

From: Dave Dameron <>
Date: Thu Jul 8 13:11:49 1999

Hi Bill and all,
At 04:41 PM 7/8/99 -0400, Bill wrote:

>OK. S-100 pins:
>On the memory card:
>Pin 68 goes to the N74LS37A pin 9 (seems to be an input pin).
>Pin 77 has no connection, right at the card edge.
> It does not go to any jumper or option pad, etc.
OK, so it expects Mwrite. Some cards had a jumper so you could select
either one.
>On the front panel:
>Pin 68 goes to U24 (8T97) pin 5 (an output pin). I
> have not verified the logic on the other side
> of that pin (which would be pin 4).
>Pin 77 goes to U5 (8212) pin 2 which seems to control
> the latch for the user data lights. It also
> seems to go into the DEPOSIT logic.

Yes, pin 77 also goes to U25, pin 1 (7400) where it is combined with /deposit.
It is then combined with Sout in another gate of U25 and outputted by U24
which is always enabled.
>On the MPU-A:
>Pin 68 has no connection, right at the card edge.
>Pin 77 goes to an 8T97 pin 9 (an output pin).
>Now that I look at it this way, this is VERY WEIRD!
>Maybe very bad? Does this mean that the CPU can not
>write to this memory card? Does the front panel
>arbitrate pin 68 for the CPU?
Yes, you write to memory with deposit or (processor write & not output)
It should work if all this logic is OK.
Received on Thu Jul 08 1999 - 13:11:49 BST

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