Cromemco 16FDC and IMSAI front panel

From: Doug Coward <>
Date: Thu Sep 20 11:53:45 2001

 "Bill Sudbrink" <> said:
> I brought this up some time ago, but never
> got a satisfactory answer...
> When I use the above combination (regardless
> of CPU board), while the system in general
> works fine, the deposit/examine functionality
> of the front panel stops working. Somebody
> said they knew of a fix, but then never posted
> anything else. I've looked at the schematics
> (I have them for both items) and can't for the
> life of me see anything that would conflict.
> Any help greatly appreciated.

 Here is some of the IMSAI front panel gottas:

 MWRITE pin 68 - This signal needs to be generated
   by one source and one source only. It is generated
   by the IMSAI front panel (by a deposit) so make
   sure this signal is disabled on the CPU board when
   used with the IMSAI front panel.

 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.

 Data Out Bus - When the IMSAI front panel does
   a deposit operation, it expects the the data
   on the Data In Bus to be reflected on the
   Data Out Bus. Some later CPU boards disabled
   the Data Out Bus to cut down on bus noise
   especially above 2MHz.
Doug Coward
_at_ home in Poulsbo, WA

Analog Computer Online Museum and History Center
Received on Thu Sep 20 2001 - 11:53:45 BST

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