RAM board for original Heathkit 8080 or Z80 CPU boards

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Peter Higgins

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May 9, 2022, 1:36:25 AM (9 days ago) May 9
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I am looking for advice regarding a 64KB static RAM board that works with a basic H8 setup consisting of an original Heath 8080 CPU with extended configuration card (or alternatively the Z80 CPU) board, H8-4 serial board, and H17 floppy controller board. I need it to replace a Trionyx M-H8 64K dynamic RAM board in a system I recently acquired. That Trionyx board (as others have also found out the hard way) was likely never designed to be stable and reliable.

The "H8-512KB RAM MMU-V40" seems to be a good option  - while it can be configured to enable only 64KB which meets my current requirements, I could use this board's 512KB and MMU should I ever want to run CPM3. Another advantage is that Todd Goodman still has some of these boards available per the listing on retrobrewcomputers. The problem with this board is that (for reasons I don't understand) it does not support running standard Heath CP/M or HDOS using an 8080 CPU per this discussion:

If the "H8-512KB RAM MMU-V40" does not work even in a basic 64K configuration with an 8080 CPU, then perhaps I should be using the "H8 8080A/Z80 64K RAM ORG0 Board" instead?

norberto.collado koyado.com

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May 9, 2022, 2:53:23 AM (9 days ago) May 9
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The "H8-512KB RAM MMU-V40" works with the 8080A CPU only if you have the extended card inserted (ORG0 board) to allow the whole 64K to be addressed. This board will only run with XCON-8 monitor.

 

The "H8 8080A/Z80 64K RAM ORG0 Board" has the ORG0 feature within the same board. Also it supports all H8 monitors.

 

Norberto

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Peter Higgins

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May 9, 2022, 9:30:06 AM (9 days ago) May 9
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Thank you for that explanation Norby. I had thought the incompatibility might have been due to a subtle bus timing issue which would be odd for a static RAM board. Since I already have an original ORG0 board and an XCON-8 ROM installed on the 8080 board, it is good to know that configuration works with the "H8-512KB RAM MMU-V40".

Douglas Miller

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May 9, 2022, 10:28:55 AM (9 days ago) May 9
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Just one note, since you mentioned CP/M 3, the versions of CP/M 3 and MP/M currently available for this board require a Z80. Long story, but basically the BIOS/XIOS is written using Z80 instructions ("sorry not sorry" as the kids today will say).

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