FDCs -- was Re: TELEDISK Problem - test-drb@ccmp.vtda.org

12 May 2001

From: Pete Turnbull &lt;pete(a)dunnington.u-net.com&gt;
...
 Which leads me to think about a tangentially-related
problem -- I recall
that some FDCs insist upon the index mark at the start of the track, and
some don't, but I can't remember which FDCs do/don't (I think WD 37C65
etc
...
 need it but NatSemi DP8473 and WD 1770/1772 don't
care). 

They all do save for the WD.  However without index you  may have
other problems.

...
 Also, I recall that some FDCs are more likely to work
with 8" drives than
...
 others, and some are more likely to work at single
density than others (at

WD had a few that were speed limited but all the 765 and later based
on that core cared less what siase save for many PC implmentations
didn't provide the adaquately fast clocks needed to run 8". that was
not a chip problem but was a board (controller) problem.

...
 least, some PC ISA controllers are unlikely to work at
SD because the
relevant components are not there).  I want to set up a PC to use with 8"

Some yes, other would easily do 8" single but not double or the reverse
case.  The older 765 PC controller designs were often PC centric,
minimalist and limited.  The 37C65 if it had the 9.6 and 16mhz external
clocks would do all modes if programmed properly.

...
 drives, including single density, mostly with 22DISK. 
I have a choice of
...
 386/486/Pentium motherboards, and a selection of ISA
controllers, with an
...
 assortment of 765, 8272, 37C65, and 8473 FDCs (I
haven't checked, but I'm
...
 pretty sure I have at least one of each).  What is most
likely to work? 

I'd go with the 37C65 board IF it has the clock logic for both 9.6 mhz
(1.2mb) and 16 mhz (all other 3.5, 5.25 and 8 inch formats).  FYI the
8272 is a 765 so no difference at all.  The 8743 is a 765 core with
some of the external logic the older 765 didnt contain on the same
silicon.
SMC did some 765 core with clock and data sep like WD37c65.  In the
end you'll find most PC controllers do not support the full 8" singnal
set,
missing are TG43, ready/fault and a few other lesser ones.

Allison