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
