View Full Version : Anybody designed a RAM card serial card combo?

September 13th, 2010, 04:34 AM
I recently received a rev 0 Altair 8800 and it only has 2 slots so I was thinking of replacing the 1K RAM card with a combo 32K RAM and SIO. Has anybody done this yet? If not, I just make myself one.


September 13th, 2010, 10:32 AM
Hi Vince,

I don't know of one being made yet. If you decide to make one, I like to suggest something about the uart for the serial port. You might want to make the serial port compatible for several different types. So that anyone with a S-100 system can use this and still be software compatible with their system, Dos, CP/M, etc.

There are about 3 to 4 types which comprised most of the software from back then. I've had to patch software to make the serial card compatible, but not everyone has this option. The original Solid State Music IO-4 was an attempt to do this, but shortly after more software was written for these other uart chips. It was compatible with the Altair, Imsai, NorthStar, and a couple others.

I've been collecting info about the S-100 cards on my webpage here at the below. I was always looking for data about this but it was always scattered about on different websites, on my harddrive, but not online, so I consolidated it all onto one webpage - it's still a work in progress -- which I have to get back to.

I started this webpage first because the serial card is the most common starting point for upgrading a system beyond the front panel. The next page will be about the Floppy controllers. This is part of the CP/M workshop material from the workshop we had back in April. This will eventually be online too.

There could be different approaches to this. One is to wire each type directly on one board -- simple but space consuming. Maybe another approach is to write an emulator using one of the AVR micro's which you can select the type with a Dip switch.


September 13th, 2010, 10:56 AM
There's enough room on an S100 card to incorporate floppy, clock, hard disk RAM, serial and parallel as well as video and keybaord interfaces. I'm surprised that no one's implemented a "everything but the kitchen sink" S100 board.

September 13th, 2010, 11:06 AM
My debug card (posted about the first version some time ago) had RAM, ROM, and an Intel 8251; of course, that's a homemade prototype. It was just RAM/ROM decoded with a 74LS138 and an Intel 8251 attached to port 0. I was going to add an 8-bit comparator and DIP switch to allow placement of the 8251 at any of the 256 addresses.

September 13th, 2010, 11:08 AM
Harte did something like this already --almost--
You can see a writeup and pic on here, it even included the CP/M Bios to support this card.
But I'm not sure if it's available any longer - it doesn't seem so.

But what's a system that doesn't have most of the slots filled anyway :)


September 13th, 2010, 03:47 PM
My goal was something simple for what I needed. I want to have memory for BASIC and a serial port using the 6850 so it will be a clone of the SIO2 (might do 2, not sure yet). I really have no other needs like CP/M, just want it to load BASIC. I may put a EPROM with a loader that will copy basic from EPROM to RAM so it can start up and run fast.

September 13th, 2010, 04:25 PM
My point in asking was that a PC board the size of an S100 is fairly expensive, while the silicon to put on it is cheap. One might as well fill the thing to the gunwales.

September 13th, 2010, 05:43 PM
Good point, not sure what else I want on there, but I'll think of something :)

September 13th, 2010, 07:27 PM
Hi! John and I made this S-100 IO board which will be available soon. It does not have RAM on it but has dual serial, USB, and voice synthesis.


With this board we'll have ten S-100 boards done and four more in the works.

Please contact me if interested. Thanks and have a nice day!

Andrew Lynch