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RE: [N8VEM-S100:2057] Using Z80 board with older S100 boards

Hi Rich,

I'm not getting a clear picture of what you've done so far, but if I had to through a guess in there, I would say the clock is too fast and your step pulses are shorter than the stepper motor can work with.  Can you jumper the Z80 board slower?  Will that jumper also affect the clock on the S-100 bus?  If in doubt, try swapping your 4Mhz crystal with a 1Mhz crystal (hopefully you will have one with a similar /compatible type/cut).

I'm reasoning out my guess with little clues like the RECAL is working, which probably sends a lot of pulses which might accumulate enough power to move the stepper motor (but perhaps not the full length of the drive, ie track 80 to track 1)

Tis only a guess.


Date: Tue, 26 Nov 2013 23:06:21 -0500
Subject: [N8VEM-S100:2057] Using Z80 board with older S100 boards
From: rich...@verizon.net
To: n8vem...@googlegroups.com

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

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