View Full Version : Suggestions for S100 debug card with 4K+ Eprom storage, RS232 and I/O disable

November 6th, 2017, 06:28 AM
Hi Folks,

I am new to this forum looking for purchasing advice for an S100 card to debug an Altair 8800 and Imsai. I am helping a buddy who has these computers reactivate them. These old units have all sorts of issues like cold solder joints, oxidized IC sockets and TTL pins and more.

I would like an S100 card that has some Eprom storage 4K min, has a RS232 Serial port (SIO) or two, some RAM and has the ability to become active on Reset and then disabled by writing to an IO port or memory address as I don't want memory/IO conflicts when I get them running.

I have debug monitors that I can program into the eprom so I believe I'm good on the software side.

I would appreciate any suggestions you have as to appropriate S100 cards for the job.

Thank you.

November 6th, 2017, 07:37 AM
Hi, and welcome here to the VCF.

I suggest that you have a look at this web site:


They have produced some impressive boards for the S-100 bus, including a system monitor board that might be helpful. Otherwise than that, if you have the front panel of an IMSAI working, that may be the best tool you can use.

Good luck!


November 6th, 2017, 09:54 AM
4K EPROM will limit your choices for an all-in-one solution. You will also want to look at compatibility with your CPU board of choice, for example some Z80 boards don't mirror the low and high I/O address bytes, which will cause problems with older S-100 boards that expect 8080 style mirrored I/O addresses.

There's no 100% solution from s100computers.com or any other hobbyist project I currently know about. We were just discussing that, w.r.t. my recent rebuilding of a couple of factory defect TDL SMB boards. I do plan on creating an all-in-one solution as you describe!

My personal vintage favorite is the Dajen SCI, but it only has 3K of EPROM (though it can program its own). It's an old design though, and does not support *PHANTOM or deselect via I/O port.

I do have either a Morrow or CompuPro IEEE-696 era board that meets your requirements, but chances are good it'll be too new for what you're wanting. You could of course modify it, but having a known good starting point is half the battle.

Have you considered a single board computer like the Vector Graphic ZCB? It's completely self-contained, the ROM monitor will run over the onboard serial port with no other cards in the system. I use one for quick debugging.

November 6th, 2017, 10:11 AM
And here is a very nice reference for your debugging endeavors:



ziloo :mrgreen:

November 6th, 2017, 11:03 AM
I personally didn't find the Bursky book to be all that helpful. It's by and far the most recommended book for getting started on the S-100 bus, but it just seemed like there was too much mostly irrelevant fluff in it. I guess maybe it's more helpful if the S-100 bus is also your first introduction to digital electronics in any serious capacity. If you do already have a good grasp of digital electronics, I'd recommend The S-100 and Other Micro Buses by Poe and Goodwin. The basic signal descriptions and short, no-nonsense explanations made it much more useful to me, personally. It also covers a bunch of other vintage computer buses. There are of course scanned copies on the Internet, but the print version is pretty cheap as a used book. I'd recommend the second edition.

November 6th, 2017, 12:06 PM
Hi Folks,
Thanks for the replies and the links.
All the CPU's in my buddies machines are 8080A's. The Eprom size could be anything up to 32KB its just that I have some old 1702a's and 2708/16's sitting in a draw and I have an Eprom programmer for them.

I have a software debugger written which with an appropriate S100 card will save me a lot of time entering in some repeat loops to scope test I/O and memory. I did the front panel gig with the Altair and it gets old quick. So far I have found that old TI sockets (silver plated tin or just tin) and TI 74xxx logic chip pins turn black and I see open circuits.

The item I am most worried about is debugging the MITS Cassette card (Piggy back) and tape deck. My buddy read somewhere that if you take the output of the cassette and pipe it into a smartphone (audio recording) that one could then use their phone with the MITS Cassette card and it should load Basic. Has that been done? If so is there a "How to" somewhere?


November 6th, 2017, 12:09 PM
I just downloaded a copy glitch.

Thank you much

ziloo :mrgreen:

November 6th, 2017, 12:41 PM
No problem! It's a very handy thing to have, I keep a copy in the workshop bookshelf and have a slightly more beat up copy that I take to vintage computer events with me.

Dwight Elvey
November 6th, 2017, 09:40 PM
As we mentioned in another thread, the Poly88 CPU board has RAM, ROM and a USART ( it would need a TTL to RS232 level shifter ). The ROM is only 3K and the RAM is quite small. Still it sounds like the board you want. It is essentially a S100 single board computer.

November 7th, 2017, 06:51 AM
Didn't one of these early S100 manufacturers tie the "data in" and "data out" pins on the bus together? I can't recall, but I do remember seeing something back when to that effect.

November 7th, 2017, 08:26 AM
I remembered something from the past and had to look it up:

1- billdeg has his own nifty and magnanimous vintagecomputer.net site.
There is an article on his site about s-100 troubleshooting using Z-80 ICE board
that might be of interest to you:


2- There are commercial as well as do-it-yourself Z-80 ICE boards that
you can look for and try,

ziloo :mrgreen:

November 7th, 2017, 05:19 PM
Hi Folks, Thanks for the new info.

Dwight where might I find a Poly88 CPU board and what is a fair price for one ?

There are some Thinker Toys SwitchBoards that have UARTs and EProm. Lots of jumpers and pins on the IO connectors. So far I couldn't find documentation on the board. Does anyone know where I might look?