osiweb.org

I finally got my Challenger III set up on the new desk in the basement. I've got a full 48K of RAM for it in OSI 520 16K boards using SEMI 4200 devices, but last weekend I traded Bill Dromgoole for an OSI 524 64K RAM board. As with most 524 boards, it has been built up as a 48K board. I haven't been able to find any documentation, but a little trace-following shows the following:

Switch Functions:

1 Enable Bank 4 (0xC000-0xFFFF)
2 Enable Bank 3 (0x8000-0xBFFF)
3 Enable Bank 2 (0x4000-0x7FFF)
4 Enable Bank 1 (0x0000-0x3FFF)

5-8 Bank select switches (leave them all ON for bank 0)

Switches 1-4 are "inverted" -- an ON disables the bank. My 524 board only has sockets for 48K populated, as that is the most contiguous RAM OSI systems support. In my case, switch 1 stays in the ON position.

I'm thinking about adding four more sockets to the board and using the prototype space to map 8K of RAM at 0xD000 for CP/M. Should be pretty simple since I'd just be driving /CE lines!

That's very cool. I've never seen one of those boards, other than on Mark's web site. It would be awesome if you posted some pics in this thread before and after, if you decide to add the extra sockets.

If I do add the extra sockets and decode logic, I'll take pictures and do a writeup on the modifications. I need to just generally document my Challenger III system as well.