8" drive on a pc controller

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sat Apr 17 09:43:41 1999

<I wasn't aware that the NEC controller chip had a problem with the step
<rate. I stuck with WDC FDC chips in my own applications.

It was a problem of how the down counter for timing the steprate was
designed. It had a granularity of 1 (8") or 2mS (5.25") and could
truncate the first(only) step pulse. There were other paybacks that
some designers really liked as the disk interface was more complete
for things like head (side) selection, drive selection. When used
with DMA it's a fairly sane chip to program. However the PC implmentation
is rather badly hacked from the start and has become the defacto standard.
If it were done as suggested ack then 8" drive would have been quite
easy to do as well.

Allison
Received on Sat Apr 17 1999 - 09:43:41 BST