jb10320@uxa.cso.uiuc.edu (Jawaid Bazyar) (01/18/90)
I'm surprised no-one has thought of this before. I'd do it myself but
I can't afford the outlay for a very necessary EPROM burner.
Here's how you upgrade your GS rom 01 to Rom 03.
Get two EPROMS (128K each I believe) and burn them with copies of the
rom 03 code (borrowed from a friends Rom 03).
Get a small PC board that will fit the two roms and their sockets. One
of the sockets should be a wire-wrap socket so the roms can sit away from the
motherboard some. The only hard part is connecting all the pins from the
non-WW socket connected to the WW socket. Well, almost all of them.
The only cute part of this is selecting which chip from the two the
processor wants, as we still only have 128K of address decode for the old ROM.
What we do is run a jumper from the one or two necessary processor address
lines to a bit of logic, which will send the proper signal to the ROMs'
chip select inputs. I guess EPROMS are open-collector (they'd BETTER be)
so you wouldn''t need a selector/multiplexer.
As far as the new hardware feature goes (what, the sticky keys for the
handicapped) that bit of code can be NOPped out or just plain ignored.
There you are. Let me know when I can get mine (with an inventor's
discount, of course :-)
--
Jawaid Bazyar | This message was posted to thousands of machines
Junior/Computer Engineering | throughout the entire civilized world. It cost
jb10320@uxa.cso.uiuc.edu | the net hundreds, maybe thousands of dollars.