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MITS 88-2 SIO Board Project

M

michaelsw

Experienced Member
Joined
May 5, 2012
Messages
56
Location
Hong Kong
Hi all,
I cannot get my Altair 8800 to talk to my laptop (Win XP, Realterm and Tera Term, using USB to DB25 adaptor) via SSM IO-4 board even with correct connection settings. Quite disappointing that it still cannot function to its max capability, really hope it can boot to Basic 4K/8K and communicate through terminal screen rather than just front panel switches.

As most of the references from the web is about how to boot using MITS 88-2 SIO board and it seems that the bootloader is specific to board (even revision, as shown in Basic manual) and Basic version and I do not have the expertise to establish dedicated bootloader for SSM IO-4 board to boot (the excellent Solivant.com bootloader instruction even could not help in my case). I still tried to follow the Solivant instruction, and it seems the laptop could connect to the Altair as I could type characters in the emulator screen, but when I sent the same Basic 4k .tag file in Tera Term as instructed in Solivant, I could only get random characters just like when the file is opened in text editor; when I send Basic 4k .bin file in Realterm, it could display Memory size+ but followed by repeated "Realterm" words and when I pressed enter there was no response except the cursor went back to the first place but not the next line and nothing happened.

I am thinking to build MITS 88-2 SIO board from scratches, as there are so many people have succeeded in using it to loading Basic and communicating with other peripheral. It seems the components used in the originals are still in the market and just think it is still possible to replicate. I know Grant Stocky has done an excellent job in replicating the Altair and the boards (I am late to the hobby and missed his great kits) but instead of waiting one (original or replica) for sales somewhere, I will make one. I am now working on CAD and hope to have one high resolution showing the back of the board, so as to finish the layout of the board. Could someone help?

Michael
 
Hi
Have you considered just adding an S-100 Serial IO board? It provides standard serial ports and USB to ease connection to your PC.

http://s100computers.com/My System Pages/Serial IO Board/Serial IO Board.htm

http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=S-100 Serial IO board

There are still a couple of these PCBs left. Also feel free to join up at S100computers.com or the N8VEM-S100 mailing list since there are several S-100 hobbyists there who probably are familiar with the topic.

Thanks and have a nice day!

Andrew Lynch
 
I have spent a good deal of time with my Altair to load BASIC and I can finally load consistently without any issues .. You must be close if you have Memory Size+. I wrote a supplement to the pages on solivant.com...go to my website and review my directions.
http://www.vintagecomputer.net/browse_thread.cfm?id=318

I suggest you try teraterm ... and dont give up yet on the 2sio you already have. The problem you've touched upon is related your terminal program and or when to be 7n1 vs. 8n1. Let me know how it goes.

Bill
 
Thanks Bill, but I don't have 2SIO, I just have one SSM IO-4 and can the same instruction be applied to it? Or is it because the bootstrap loader (from Solivant) just does not work with SSM IO-4 card? I use 8/n/1 by the way in the whole download process and switch to 7/n/1 after the download and attempt to talk to the Altair on the screen. No luck..
 
What port is the ssm set to use? It seems like if you get a "Memory Size+" message you're in good shape and you can use the SSM card as is. Try the terminal program teraterm per my site or solivant.com. An orig MITS 2SIO is very hard to find.
 
billdeg said:
It seems like if you get a "Memory Size+" message you're in good shape and you can use the SSM card as is.
Click to expand...

I agree that it doesn't sound like the IO card is the problem if you got this far. Dumb question: you do have an 8080 CPU, not at Z80?
4K BASIC doesn't work with a Z80 and hangs at some point at start up.
 
I am not sure what port is used, but it communicates with my laptop (both Realterm and Teraterm) via COM4, and I have set the card to simulate "MITS interface card REV 0" and main console is Serial A at ports 0 & 1. With the same bootstrap loader, I get "Memory Siz+" only but not further with Realterm using Basic 4K bin file from www.theoldcomputer.com. Using the .tap file from Solivant with Teraterm for the same bootstrap loader, I only get strings of strange characters (just like the file is opened in a text editor) and it seems the code is not executed and NO "memory size" is displayed, the same happened when I tried to send the tap file in Reatterm.

My CPU board is MITS Rev 0 with C8080A. My idea is if I cannot solve the problem, I will make MITS 2SIO board.
 
Wrong port. I am talking about the s100 port not pc comm irq port. I see no evidence that it's not a modern pc terminal issue. Making a s100 serial card is a huge project compared to getting your pc terminal software to operate correctly.
 
Hi Bill I will take some picture of the connection and the screens to explain. By the way, when Solivant.com and you mentioned 8n1 and 7n1 conversion during and after the loading, do you mean I just need to change the setting in the Teraterm only or I also need to change the setting physically on the card while the Altair is still on?
 
Yes. When you see the "Memory Siz+" or whatever that means you have a slightly off terminal setting, but the program has been loaded correctly into the computer. Just change TeraTerm from 8n1 to 7n1. After that if you hit enter, it should allow you interact with BASIC. Nothing more is needed on the Altair, no changes, no need to touch anything.
Bill
 
billdeg said:
Yes. When you see the "Memory Siz+" or whatever that means you have a slightly off terminal setting, but the program has been loaded correctly into the computer. Just change TeraTerm from 8n1 to 7n1. After that if you hit enter, it should allow you interact with BASIC. Nothing more is needed on the Altair, no changes, no need to touch anything.
Bill
Click to expand...

With the SSM IO4 the problem is most likely the status word configuration. I had very similar issues to this. I could get basic to load but it wouldn't output properly to the terminal. The key to correcting this is to wire the status word on the SSMIO4 to replicate the 88-2SIO. In short on the SSM IO4 DAV/ODA needs to be set to bit D0 and and TBMT needs to be set to bit D1. See my guide on it under: Status word configuration, sockets W2 and W1
 
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