28 Nov
2015
28 Nov
'15
9:23 p.m.
On 11/28/2015 06:57 PM, Fred Cisin wrote:
WD style: no problem with index pulse timing relative
to data NEC765
style: index pulse is necessary during LLF, but may need to be
blocked during read/write, although a few of the newest drives may
not be happy without index.
765/8272 are particularly bad in this respect (they're blind for a full
millisecond or so) in contrast with 765A/8272A, which chopped the blind
spot by half.
In the 8272 days, I added a one-shot to delay the blind spot by a
varying amount, which solved the problem neatly, while still allowing
the index to pass through.
The index is also needed for WD17/27 family controllers also for LLF.
Ya gotta start (and end) somewhere.
If you simply block index with the 765 type FDC, you'll never get a
"sector not found" error--if you have a deadman timer, it'll expire.
--Chuck