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Using Z80 board with older S100 boards

All —

I’m using the Z80 Master board with a custom EEPROM for a “test” system for my IMSAI — I try a bunch of stuff out on it first before putting it in my IMSAI. It works pretty well for prototyping. Anyway, I’m putting a floppy disk system together to match my IMSAI — a CompuPro Disk 1 and two 5.25” HD drives (which emulate 8” drives) — so that I can do some other testing.

Is there any trick to getting old boards to work properly with the Z80 board? Everything is configured identically between the systems (the same console, memory, disk cards and identical floppy drives). I’ve swapped everything around, including the drives, and proven that the hardware works, so it has to be the Z80 card interacting with the Disk 1. The Z80 is set for 4MHz and all of the jumpers match the pictures. I have 1WS for memory and ROM and 2WS for I/O.

The actual symptom is that the floppy drive isn’t track stepping. Everything else is fine (memory access, console I/O, booting, etc.) and it does respond to certain commands such as RECAL. I checked the cable for signal continuity and it’s fine, too.

Any pointers, hints, tips or clues would be appreciated. Thanks! 


Rich Cini
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator