8 Nov
2007
8 Nov
'07
12:35 a.m.
Changing the crystal would half the data rates making
it right for
5.25" floppy.
One of the modes all the contrllers that use hang mode (wait), is
sector never found. Wrong clock rate will insure that.
I was also considering that at 2MHz instead of 4 the FDC controller
will be operating close to its limits and may need the wait
state. What was happening was probably a missed wait state.
Both work. The logic however uses the 8T97 and
tristates it when
not needed (board not addressed) which is a "legal" way to do it
though it seems like more effort.
Of course using high is active and mixing than with low is active was
a dumb thing too. Even Tristate asserts a better low than a high.
The front panel buffer is hard wired on, so the Tarbell was shorting
out the panels XRDY.
I reviewed the 1k memory card and it does tristate it like you
said. My problem with the 1k card way back then was that the MITS
documentation puts both on the PRDY line. In my two systems this was
no good. The transients would corrupt the bus cycle. This was found
when working with an altair laying on a wooden table. It wasn't in a
metal case. I never tried putting both on the PRDY line when it was
in an enclosure. I imagine it would have worked better in the case
since I've never read any errata on it, but I wanted to play it safe.
If you want to talk about media abuse...1.4MB disk with the HD hole
covered, formatted to 71k : )
One of my problems MIGHT have to do with the 16v and 8v supplies not
turning on at the same time. I will have to investigate that more...
Thanks,
Grant