MITS 88-2 SIO Update

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	by Bill Degnan - 03/03/2010 02:22
I re-jumpered the 2SIO card that was pointing to port 000 to 020 and installed it into my Altair 8800b. I have toggled in the 1st stage loader from the manual and I get the expected lights/results. I was able to toggle in the little echo character program to verify that that the card is correctly interfacing on port 020, the standard for MITS I/O and MS BASIC. I found a great web site that walks a person through the process of testing a 2SIO card and downloading programs through it into RAM of the computer including BASIC: http://www.solivant.com/...air_bootloaders&pagen=0 On page 4 or 5 in the bootloaders section it talks about the cause of "MMM's" being printed on the screen during download of a program. This is what's happening to me, the program can't find the RAM location to dump the program. I verified that I do have RAM available in all 64K pages (0000 through FFFF), but I need to run more substantial RAM testing to be sure it's working correctly. I need to check to see where BASIC is being loaded. Per solivant.com I attempted to download just the 2nd stage loader, and I determined that it's not being written into memory correctly, and it bombs around 1300 bytes into the import consistently. It may be that the RAM I am using is not compatible with the tape download, or it's protecting the addresses I need to write to. I also have a MITS PROM card with MBL PROM which has different switch settings than the toggled-in version, which leads me to think that they're different. Using this loader I attempted to emulate the papertape load of just the BASIC 3.2 code, but I get no response from the computer. I *think* I have the correct switches set before running this version of the loader. Next - I will test the RAM and if necessary plop the cards into a different computer. Reply

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