IMSAI 8080 (our show so far...)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Jun 29 15:01:56 1999

Have you contacted Todd Fisher at www.imsai.com? He might actually know
about this type of problem.

Dick
-----Original Message-----
From: Dwight Elvey <elvey_at_hal.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Tuesday, June 29, 1999 1:19 PM
Subject: RE[2]: IMSAI 8080 (our show so far...)


>"Bill Sudbrink" <bill_at_chipware.com> wrote:
>> Ok. There is a 16 pin ribbon cable between
>> the front panel and the MPU-A card.
>
>Hi Bill
> I'm sure there is a scrambling of this connection
>someplace. This is the only place that can do the
>things you mentioned. The front panel is hard
>wired to the S-100 bus. This means that wires can't
>get mixed here. The data lines from the CPU board
>to the front panel can get swap around. Remember that the
>way the front panel does things is by jamming instructions
>and data directly onto the CPU's bus through the cable.
>The results are read from the S-100 bus. In other words,
>when you use a front panel switch, like examine, it
>forces a jump instruction into the CPU with
>the address you specify with the switches over the cable,
>in sequence. A real clever trick I'd say. You'll note that
>the C3 bit sequence still works if the data bits 7-0 are mirrored
>to 0-7. This is why the panel seems to do anything at all.
> If reversing the ribbon connector in the header doesn't
>work, try removing the socket from the CPU card or front
>panel and installing it on the other side of the PC
>board. I would suspect that this was an error in the construction
>of the front panel from day one. It is most likely the
>front panel that is backwards. Just flipping the IDC header
>on the cable won't mirror the wiring to the connector.
>Putting the socket on the other side of the board will
>mirror things.
> At worst, you'll have to hand wire the cable to make up for a
>non-standard connector but I'd think it was more likely
>just getting the header socket right at both ends. I don't
>have a schematic of the panel in front of me but it is a
>simple mapping problem.
>Dwight
>
Received on Tue Jun 29 1999 - 15:01:56 BST