PDA

View Full Version : IMSAI 8080 help



thefoolonthehill
November 22nd, 2005, 05:15 PM
HELP! I just got an IMSAI 8080 from one of the "founders" of the computer industry. It shows me all signs of working but I can't find out what's wrong... It has the original 8080 processor card in slot 0 and a "not" original RAM card in slot 3. I can read the RAM and run whatever program is generated randomly but I cannot program it my self! I'd like to use the switches to program it but the deposit switch doesn't write my input of the switches into the data bus.

The RAM I have is the IMSAI 16k static RAM. Anyone know what the heck is wrong with my computer?

Erik
November 25th, 2005, 12:20 PM
I'm not sure what you mean when you say the machine works but that you can't deposit into memory.

If you don't know what's there, you can't be sure what you are getting out is right.

My best guess would be that your RAM card isn't fully functional. I've got about 2-3 MB in older S-100 RAM cards and I can usually be sure of about 128K or so in one of my S-100 machines! The rest are flakey or busted outright.

Your best bet would be to either find a "known good" RAM card or to find another way of testing the one you have in a known-good machine.

The second most likely failure point is the front panel controller which may be mangling the signals to the bus.

Best of luck!

Erik

thefoolonthehill
November 25th, 2005, 01:35 PM
well I mean that by "when I turn on the computer the ram has random information in it. But I cannot deposite information while programming it, like when I enter an assembly language command, I can't feed that information to the data bus."

Erik
November 26th, 2005, 06:09 PM
well I mean that by "when I turn on the computer the ram has random information in it. But I cannot deposite information while programming it, like when I enter an assembly language command, I can't feed that information to the data bus."

You're still dealing with either a dead RAM board or a bad front panel board. You'll either have to break it down with a 'scope or find a known-good RAM board to isolate that.

E

thefoolonthehill
November 27th, 2005, 05:03 PM
Yeah I was thinking of doing that next weekend. Because I have the extender board, and a decent scope.