8 Oct
2007
8 Oct
'07
2:23 a.m.
Tony Duell wrote:
Looked some more and it seems that power switching is done to stop a
PROM output being shorted by a 74ls05 output !
i.e. An input ot the 74ls323 is either driven by the Stateprom, or
pulled low by the ls05 . That is indeed two outputs being shorted.
And this is supposed to be a clever design....
When
backengineering it I found that both Proms and the 74174 have their
power switched. Why would that be ? seems very hairy to me.
Yes. This was a typicval Apple method of saving power. No matter that
it's a made idea to paply logic signals to an unpowered chip. And people
wonder why I dislike Apple hardware designs...
Is there anything I could easily type (pinouts of the
slot, pinouts of
the drive cable, etc) that would help you?
Thanks, meanwhile the problem has been traced, with a bit of luck, to a
bad connection between 2 pcb's in the floppydrive itself. I was able to
copy Kermit across and am now happily downloading my second Lilith disk.
Jos