Rev 4 CPU board only works with on-board RAM
glenn.f...@gmail.com
I am trying to get my Rev 4.0 CPU board to work again with the external RAM board (512K, Rev 1.2). This used to be a working configuration, but it’s been a few years. This will allow me to run CP/M 3/Plus (again this used to work).
The CPU board works fine when jumpered for internal RAM.
The 512K MMU board seems to work fine. I installed it in my Rev 3.1 system and it comes up and passes Doug’s TEST512K program (I don’t have a configuration for that system to run CP/M Plus so didn’t go that far).
When I change jumpers JP15 (DISable PCB RAM) and JP18 (“H8-BUS”) the CPU fails to come up with the 512K MMU installed (only RUN and PWR LEDs are on). I’ve also tried other RAM boards (e.g. Les Bird’s old 64K board and Norberto’s H8-64K board) but sane thing happens.
Here’s a detailed picture of the board (with the DUART board removed to expose all jumpers):
https://photos.app.goo.gl/4WK7Fhq4gyTFcr938
any suggestions on where to look or how to debug this? Thanks.
- Glenn
norberto.collado koyado.com
Interesting! Let me check my board.
Norby
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norberto.collado koyado.com
Hello Glenn,
I reconfigured my Z80 board to use external RAM. Did not install the external RAM board and on power-on only RUN and PWR LEDs are on. Then installed the external RAM and system booted fine.
Please check/replace the JP15 (DISable PCB RAM) and JP18 (“H8-BUS”) in case they are bad/broken.
Thanks,
Norberto
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norberto.collado koyado.com
Also, it could be a cold solder joint related to such circuit.
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Glenn Roberts
On Jan 24, 2025, at 11:37 PM, norberto.collado koyado.com <norberto...@koyado.com> wrote:
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