Roger, before you give up let me take another try. I need to know in detail however your setup
What Z80 board, what S100Computers boards. What Phi, clock speed.
Can you get to an absolutely minimum system Z80, RAM, Console I/O and V3 IDE.
Did you say you also have tried V1 & V2 boards, (if so that makes me suspicious you have some other board with a port(s) overlap).
You say you cannot write to the 8255. What about configuration writes? Check by setting port A or B up as simple input ports. Tie one or more pins high/low and see if you get the correct input data. Let me know answers to the above before I go further.
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com]
Sent: Tuesday, July 14, 2015 7:09 PM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:7405] Re: V3 Dual IDE/CF S100 Bus board initial checks
Hi John,
>> Those IDE boards are in fact a very simple boards.
I agree! On paper, at least. But all the chatter I've seen here w.r.t. the flavor of 8255, mods. to the boards, and subs. for some of the standard LS logic, leads me to believe that they are not all that straightforward.
>> Using a simple logic probe determine if the chip CS* lines is going low with a write.
It is.
>> If WR* is going low etc.
It is. Everything looks OK (with a simple logic probe), but I can't see these signals in relationship to each other (no digital logic analyzer).
>> Single step through a simple continuous write loop in RAM. Eg:-
Yep, did that. As I said, a simple loop to read from any of the 8255 ports seems to work OK. But, I can't see any output at any of the ports using a simple output loop. And, yes, I initialized the 8255 for input or output before running these loops.
>> By now there are well over 100 of these boards out there. It must be some glitch in your
>> system
That's what I can't understand -- my backplane (CompuPro) works fine with lots of legacy CPU's/FDCs/etc. N8VEM serial card works great in the backplane. I'm giving up on the CF cards for now ... can't spend any more time on this.
Roger
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