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  Processor Tech General Purpose Module by Bill Degnan - 09/20/2009 22:05
For my own reference, I took some pictures of Bill Sudbrink's Processor Tech General Purpose Module card, which is similar to mine except that he made some modifications to protect some of the F000+ memory when CUTER and NorthStar DOS try to use the same spaces. Here are the pictures I took:
Processor Tech General Purpose Module Mods for NS DOS and CUTER

Of course now I have a problem with my CUTER program, I must have blown an IC. Next - find and repair the bad component.


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  IMSAI 8080 with CUTER and N* DOS by Bill Degnan - 09/26/2009 22:07
While at the Vintage Computer Festival I was given a NS* disk with CP/M BIOS edited to work with CUTER. My GPM is wired quite wildly, but it works (until I screwed something up), and I could get a prompt and load programs by entering machine language through CUTER.

I am no longer able to boot a known-working Northstar CP/M disk in a known working drive with a known working MDC-A4 driver card. If I remove the GPM card and jump to the loader address I can hear the disk loading, but I have to rely on the GPM for screen and keyboard I/O.

I took pictures of a another working GPM card so I could compare the two. I noticed that I did not have the same jumper connecting aa to L.

I should have been more thorough, but I decided to jumper my GPM card's aa and L. When I tested this configuration it must have caused a fault because now the previously working Processor Tech GPM card, with CUTER in U9, does not display the prompt.

When I boot CUTER the program (attempts to) loads, but the prompt freezes at the solid block stage when CUTTER is initializing, before the > prompt.

The closest IC to the U9 jumpering disaster is the the SN74LS367N in the U18 socket. I hypothesize that this IC could be bad as a result of my jumpering (or one of the components near by).

I have to figure out what I may have fried.

BUT FIRST, let's see if the CUTER program is loaded into memory. The first byte is located in C000 and is a 7F = START

Here is a complete listing of the machine instructions for CUTER (CUTER)
http://www.sol20.org/programs/cuter.orig

I verified that CUTER is loading into memory. I checked the first 35 instructions and there was a 100% match.

Next I single stepped through the code, here is what happens. Starting with the 77 00 23 below it loops endlessly (marked with the dash chars below.

7F
C3
D7
C1
AF
4F
21
04
C8
77 -
00 -
23 -
06 -
C2 -
D6 -
C1 -
06 -
C2 -
D6 -
C1 -
77
00
23
06
C2
D6
C1
77
00
23
06
C2
D6
C1
77
00


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  PT GPM card - further attempts to fix by Bill Degnan - 10/17/2009 00:34
UPDATE - I swapped the SN74LS367N in the U18 socket and changed out the 7805's, but this did not help.

Maybe there is nothing wrong with the GPM card, it could be something else I suppose.


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  Further attempts to fix PT GPM card by Bill Degnan - 10/18/2009 20:06
VDM-1 swap
I also swapped out the VDM-1 card with another (and in the process fixed a third one). No change.

Next:
replace the 91L02 RAM or substitute with 2102L1PC or 21L02B RAM

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