I wire-wrapped a simple EPROM circuit on a N8VEM buffered prototype card. (Very nice card, BTW! Easy to work with.) It is just a single 27C256 EPROM that can be phantomed out by doing I/O to port "FF". I have a couple of Digital Research (Computers) 64k static RAM cards with a half phantom feature. Lower 32k can be phantomed out. The wire wrap circuit works very well with a CompuPro CPU-Z. On power up, or reset, the EPROM is in the memory map, and it goes away when I write to port "FF". It's a toggle, actually, so it can come back again with additional I/O to "FF".
Unfortunately, it doesn't work at all with *any* of my Cromemco ZPU's (revs. C, E, and F). Very disappointing. That is where I *really* wanted it to work. It also won't work with a couple of NorthStar CPU cards I tried, and a CCS 2810A CPU card. I'm not terribly surprised about the NorthStar or CCS. They are *very* old, and I doubt that they are 696 compliant. The Cromemco CPUs did surprise me. The CompuPro card was advertised as 696 compliant, but I'm not sure about any of the others. It is a very simple circuit. Besides the address and DI buses, it only uses sMEMR, sOUT, sINP, reset*, and pDBIN. Oh, and of course, phantom*. The only cards in the backplane (CompuPro 20-slot) are the wire-wrap EPROM card, the 64k static memory card, the CPU, and a N8VEM serial card (for console). So, my question is: is there any particular place to look for 696 non-compliance problems, or is that a total bucket of worms? I wonder if there are any "tweaks" I can make to the Cromemco ZPUs to get them to work with the EPROM card? Anybody know what might be the problem here? Roger -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
