14 Sep
2005
14 Sep
'05
5:04 p.m.
the original IBM PC Bios was a Motorola 24 pin ROM. In the early
days, I used a 28 pin socket and wired to a 24 pin header to be able
to modify the bios and use a standard 28 pin EPROM for changes. There
were no latches in the ROM. It was probably cheaper for IBM to get a
masked ROM then to use EPROMs which were relatively expensive for the
quantity they were buiding. There was no EPROM equivalent for the
Motorola chip.
best regards, Steve Thatcher
Yes, as I understand it and saw, the roms could be enabled, using a
line that the data I/O didn't drive (29b variety any did not). So you got
FF out when you read them.
I can believe there were some odd enables on those ROMs, but I wasn't
aware of any internal latches. I will have a look again.
The PC used either EProms, (16K I think) and the
Roms that were
shipped with the BIOS were registered. The standard Data I/O would
Do you mean there were internal data latches in the IBM ROMs?