22 Aug
2015
22 Aug
'15
5:20 a.m.
On 08/21/2015 06:46 PM, Jay Jaeger wrote:
One other thing I have noticed is that sometimes after
a read problem
on the bad drive the FD 1791 floppy controller chip seems to get into
a "snit" that even a reset does not cure - I have to cycle power to
get it back. Now that I have a reliable drive as the first drive, it
is clear that this is not a reinsertion / wobble issue. So, I will
have to check the reset line going to that and the PIO chip that
supports it to see if there is a problem on the board. I also have
some spare FD 1791's I can try, that are of a slightly later
revision, to see if the problem is related to that specific chip.
Try a later revision of the 91. We had miserable problems with the
WD1781 (the FDC that no one has heard of) and eventually had to
incorporate an external register bit into the design to enable software
to do a "hard" reset of the 1781. It could occasionally just go deaf
and dumb; WDC knew about the problem and that was the only solution offered.
--Chuck