2 Sep
2022
2 Sep
'22
3:22 a.m.
On 9/1/22 18:43, Mike Katz wrote:
> Taking my memory back to the early 1980's and the Western Digital floppy
> disk controller chip family (177X single density and 179X double
> density). I wrote the 6809 drivers for Gimix Flex. The controller chip
> used the index pulse for sector zero position and for timing out a
> failed read or write command. I don't recall if that controller chip
> family could handle hard sectoring (one hole per sector) or not.
On Thu, 1 Sep 2022, Chuck Guzis via cctalk wrote:
All WD and NEC floppy controllers use the index hole
for formatting as
Fred mentioned. Further, I believe that three passes of the index hole
while attempting to read or write gets you "Sector not found" if the
address ID isn't detected. See datasheet and app notes for details.
OB_Obscure stuff:
At least some of the Teac 5.25" FD55-x series drives ALSO used the index
pulse for determining "drive ready". If you mask off the index hole
with a write protect tab, then those drives will give DRIVE NOT READY.
So, on THOSE drives, masking off index pulse (for disks (such as come
Cromemco) with first sector too soon after index, etc.) should be done by
interrupting that pin of the cable, or modifying the FDC controller board.
(ANY masking of the index pulse will "corrupt" the FDC's guesses of what
an error is)
On a bet, . . .
we noticed that the Central Point Option Board software could not work
without index pulse. You CAN modify a drive to index off of the spindle,
without an index hole. FLIP a hard sectored floppy, and format it with
indexing off of the spindle. THAT disk can now be read and/or written.
But, the Central Point board software can't handle it. Punching an index
hole access hole in that flippy won't help, because the disk is hard
sectored. Thus, a disk whose content canbe copied with COPY or DISKCOPY,
but not with the Option Board (with supplied software).
No WD or NEC floppy controller handles hard-sectored
recording schemes.
But, how about a WD TRACK READ with the index pulse masked?
HOWEVER:
A few years back, I was sent a bunch of 8" HS disks that were really
puzzling--the sector ID address headers didn't line up with the sector
hole timing. In fact, they were WAY off.
It turns out that some 8" drives can be set to separate the sector holes
from the index hole (separate output pins for index and sector). Doing
so, gives you what amounts to a soft-sectored floppy, regardless of what
the physical object is. I know that I used a Siemens FDD-200 drive
jumpered accordingly to read them.
Good times.
--Chuck
COOL!