14 Sep
1999
14 Sep
'99
3:08 p.m.
<There are some UMC parts that have the disk controller + data separator +
<precompensation, etc on the same chip. At least some of those claim to do
<single density in the data sheet, but fail to work properly in practice
<(the failure is a little odd -- the chip will find the sector and it will
<attempt to read it. But the last byte will be mangled, something like that)
One of my hacks is to use ISA boards like Hard disk controllers, FDCs and
others as "modules" for other busses and I've used boards with UMC supper
chips for standard modes including FM with ease. One of the problems is
most people don't know much about programing 765 cores.
<There are no pins for connecting an external data separator either.
Not needed. You have to set up the auxilary registers for the right clock
rate and precomp for FM.
<I don't know if you can kludge them to do single-density. Maybe decode
<the FM data externaly, re-encode it as MFM and fiddle the data rate :-).
<A heck of a lot of work, though.
Not required.
<I assume that the UMC 8272-clone (there is one, just a plain 8272 with no
<extra logic) will handle FM with the right external data separator, though
Yep an 9216 or similar works though the counter based design used on DTK
and some of the older compaq boards works fine if the clocks are correct.
Some of those ISA-8 boards using 765A or 8272 (and clones) are easy to mod
for most any data rate and mode. The lines to the chip for those functions
are (MFM, RDD, RDclk, VFO, WDD, WClk, WREN, PS0, PS1) and should be easy
to follow on some of thse boards. The 9216 or 9229 can do all modes and
the only thing remaining is to maybe change the crystal.
Allison