Cromemco 16FDC and IMSAI front panel

From: Frank McConnell <fmc_at_reanimators.org>
Date: Thu Sep 20 13:09:00 2001

Doug Coward <mranalog_at_home.com> wrote:
> PROT & UNPROT pins 20 & 70 - The IEEE 696 standard
> says that these pins will be at ground. Some
> motherboards ground these lines. But grounding
> these pins on the IMSAI front panel will disable
> the front panel. To fix this, cut the traces,
> on the front panel, right at edge connector
> pin 20 and 70.

I'm thinking that some CPU boards expect the front panel to ground one
of these signals when the panel is putting something on the data bus
via the panel connector (and the CPU board should therefore use the
data bus on the panel connector instead of the one on the
motherboard). Maybe I am confusing this with some other signal?

I ran into this in 1989 with a CCS Z80 board and no-name chassis
with apparent 696 motherboard. Took me a while to figure out why
it wasn't coming up.

-Frank McConnell
Received on Thu Sep 20 2001 - 13:09:00 BST