20 Jul
2007
20 Jul
'07
4:16 p.m.
A friend of mine and I collaborated on a version in
2003 that 'almost'
worked for me, and I wasted a lot of time trying to figure out what the
problem was. Recently I decided to revisit it and after the last two
days I figured out that even though the capacitors are probably nice,
the thing that was holding me back was the lack of an OSC signal from
The OSC signal was the 14.3xxx MHz master clcok signal in the PC and XT.
IBM specifically state in the Techref that it has no gauranteed pahse
relationship to any other signal. In the expansion unit, it's provided by
an oscillator circuit on the expansion backplane, in the PC/AT, it's
provided by a separate oscialltoer circuit (i.e. not in any way
associated with the CPU/system clock) on the motherboard.
It was used, of course, by the CGA card as the master clock for the video
and colour cubcarrier timing. Some other cards used it, often divided
down, as a master clock.
the Jr. The cards that I was using (SCSI cards) were
dependent on it,
and we left that pin on the ISA slots not connected because we didn't
have that signal available. An NE1000 Ethernet card (which does not use
I think I'd jsut ass one of those 4-pin oscillator cans and be done with it.
-tony