>> Roger, before you give up let me take another try.
>> I need to know in detail however your setup.
OK .... it will take me a little time to re-create my attempts to get V3 working, but I can give you a little info. about what I was doing before I pulled the cards out. CompuPro backplane, with CompuPro CPU-Z80 (running at 4 MHz). The CPU-Z80 has provision for two on-board EPROMs, and I'm using (for now) two 2716s burned with a simple monitor that lets me look at memory, change memory, jump to a given address, download code, etc. I'm using a 64k static RAM card (Digital Research Computers) based on the 6116 SRAM. And there is a N8VEM serial card in there too. I believe it is configured to run at port addresses 0Axh (but I need to check that).
I seem to remember (it’s a long time ago) I actually ran the V1 board diagnostic with that CompuPro Z80 board. So it should be OK.
>> Did you say you also have tried V1 & V2 boards,
Yes, believe it or not, I came closest to getting things to work with the V1 card. I got the single CF MYIDE code running, and it seems to behave normally, at least for reading the CF card. There is some kind of an issue with sector numbering (what it displays as the "first" sector is really (I think) the second sector), but as I remember it, there was a discussion about that. That MYIDE jumps the sector numbering by 1 to take care of CP/M sector numbering?
If you got the V1 to work then the problem must be in the drive select circuit. Code/timing to the 8255 is identical for both boards.
Try forcing drive A on that V2 board. Bend out pins 5 & 6 of U16. On the back jumper pin 5 to +5, pin 6 to ground.
My attempts with V2 were a total bust.
>> You say you cannot write to the 8255. What about configuration writes?
Well, that's interesting. I *thought* that I was sending the correct configuration codes (80h for reads and 92h for write to port A?) to the control port. BUT, what if that is not working, and the 8255 comes up in some sort of read configuration? Then I could read OK, but writes would not work. That's what I'm seeing.
>> Check by setting port A or B up as simple input ports.
OK, give me some time to set this up again, and verify that's what is happening.
Need to know what you got here.
As a longshot see the bug report on the S100Computers page for modifying the GAL 1. Try that.
Roger