SS-50 1MB RAM board – Retro Computing

One of the really cool things about the SWTPC 6809 CPU board is the ability to extend the 64K memory map to a full megabyte by use of Dynamic Address Translation (DAT). I’m not convinced many people actually had more than 64K back when SWTPC was making their CPU board, but when I designed the Corsham Tech 6809 one of the features added was 128K of RAM.

It seemed natural that people with either our CPU board or the original SWTPC board would want to use the extended memory scheme, so it didn’t take long for us to design this 1 MB board.

There were no existing memory boards to model the design after so this was done based on looking at the CPU board schematics and the crude description of how DAT worked. A number of customers have confirmed this board works well in OS/9 systems, as well as our XMEMTEST extended memory test program.
Features

• Fully compatible with the DAT design.
• Supports A16-A19.
• If not all four extended address bits are desired, any of them can be ignored.
• Each of the sixteen 64K memory banks can be enabled/disabled via switches.
• RAM chips are static. No refresh logic.