John --
>> The board has 60K RAM, 4K ROM, IOBYTE port and a Z80/S100 bus circuit. The board actually has 128K of RAM (2X64)
>> but I cannot figure out how to switch banks without blowing the software out of the water for CPM3. Sure I can do so
>> within the ROM but how do you get stuff across from one bank to another. Anybody seen this done. Normally you have a
>> 16 or 32K window that switches. Hate to settle for a 60K non banked CPM3 system!
Use a single 512x8 SRAM chip and a 74LS670. I've built an Z80 SBC prototype with the 670, and I think it would be easy to set one up with either 16k or 32k banks (user selectable) with just a few jumpers. With 32k banks, the CPU would use the whole SRAM chip, with 16k, just half. Worked great on my SBCs, at 10MHz. Both banking schemes seem to have advantages and disadvantages.
Roger