Re: [N8VEM-S100:7280] IEEE 696 compliance/non-compliance

Roger,

The *Phantom signal is only needed as an input on a RAM (or Eprom) card.

*Phantom is used to disable output to the S-100 data bus when another card says

it needs access to send data to the bus (asserts *Phantom low).

CPU boards with no on-board memory do not need *Phantom. The ZPU board is

an example of this.

The CCS 2810 CPU has an Eprom socket on it, so it does input *Phantom.

There is a *Phantom Enable jumper on the CCS 2810 board.

The CPU-Z board disables the S-100 Data In buffers when it’s Eprom is addressed, and

the Eprom is enabled. So it won’t have a conflict with off-board data when reading

it’s Eproms.

Don’t know about Northstar, some boards had an Eprom, many did not, and then did

not have the Eprom decoding/enable circuit installed on the board.

The N8VEM buffered prototype card address decoder seems to have been designed

to decode 8-bit I/O port addresses, so only the low 8-bits of address were needed.

To use it for memory decoding, you probably need to cut the 8 low address traces to

the 74LS688 chip, and wire by hand the upper 8 address lines (in order: A8 thru A15).

Then correctly hook up the *Phantom signal. Attached is part of a conversation I saved

that explains how to assert *Phantom from an Eprom *CE signal to the S-100 bus.

Regards,

Rick

From: norwestrzh via N8VEM-S100

Sent: Saturday, June 20, 2015 8:02 PM

To: n8vem...@googlegroups.com

Subject: [N8VEM-S100:7280] IEEE 696 compliance/non-compliance

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