9 Aug
2013
9 Aug
'13
5:05 p.m.
On Fri, Aug 9, 2013 at 5:00 PM, Glen Slick <glen.slick at gmail.com> wrote:
Does track 43 control both precomp and reduced write
current, or only
reduced write current?
The write precomp is done in the controller, while the reduced write
current is done in the drive. In early 8-inch drives, the reduced
write current was done based on the TG43/RWC signal on the interface,
but in later 8-inch drives the drive electronics does that on its own
and ignores the TG43/RWC signal from the controller.
Older floppy controller chips provided an early and late signal along
with the write data, and it was up to external circuitry to implement
the appropriate delays based on the early and late signals. It was up
to external logic to determine whether or not to apply precomp, and
how much (typical 125 ns for low density 5.25 inch, and 63 ns for high
density). For 5.25 and 3.5 inch, it was common to apply precomp on all
tracks, though fancier controllers used a bit on a separate I/O port
to allow turning precomp on and off. Certainly TG43 wouldn't be an
appropriate signal for precomp enable on 48 TPI 5.25-inch drives.
Eric