Micom SRAM and DRAM Boards

I was a member of the West Coast Computer Society (WCCS) right from its first meeting in September 1976. Another member was Jack DuMoulin, who was with a local electronics company, Micom Industries Inc. Their products included two memory boards that I bought for my computer systems. Jack retired to Salt Spring Island, and passed away December 26, 2006.

EXORbus 8KB SRAM

The first board I bought from Jack DuMoulin was an 8KB static RAM board for the Motorola EXORciser bus (EXORbus). I bought it as a bare board and assembled it. I used this with my MEK6800D1 system. I didn't keep any information on it when I sold it decades ago, and haven't found any pictures. It probably had 64 SRAM chips (2102: 1024x1 16-pin NMOS), so drew lots of power.

SS-50 Bus 64KB DRAM

Five or six years later I bought a second board from Jack DuMoulin. The DR8264-68 is a 64KB DRAM board for the SS-50 bus that I installed in my SwTPc 6809 system. I bought it as a bare board and assembled it. It draws less power and generates less heat than the two SRAM boards (SSB 16KB and DRC 32KB) it replaced. It also supports extended (20-bit) addressing, although I didn't enable that feature. It uses RC controlled one-shots to generate the /RAS and /CAS signals, which isn't ideal, but I seem to remember it ran reliably in my system. (And almost 40 years later it still works!)

Memory can be disabled in 8KB blocks to avoid contention with other boards in the system. I wish it used 4KB blocks instead, as 8KB memory is now wasted ($9000-$9FFF and $E000-$EFFF) that could otherwise have been added to user RAM, giving me the maximum 48KB ($0000-$BFFF) instead of the current 40KB ($0000-$9FFF after the MMU/DAT has moved pages).

(Click on a picture for a larger version.)
Pictures of Micom 64KB DRAM board. (190-931KB .jpg)

I found two slightly different sets of documentation for this 64KB DRAM board. The first schematic is probably the modified "as built" version, since I made some modifications to the board.

Micom 64KB DRAM board schematic drawings, assembly instructions, and modification instructions.
(2.2MB PDF scanned image)

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Last revised 2021-Nov-11 11:47 PST.
Copyright 2021 by David C. Wiens.

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