9 Aug
2013
9 Aug
'13
6:41 p.m.
On 8/9/13 3:46 PM, Al Kossow wrote:
I suspect Chuck Guzis is very familiar with all of
this. I also thought that on floppies precomp
was only applied after tk 23 on 5" and 43 on 8"
Did some more digging around to try to remember where I had gotten that idea from, and
turned up
http://home.earthlink.net/~z100lifeline/data/Z207Cal.html
which is unique to the Z-207
Precompensation Calibration
Write precompensation corrects for "bit shift" distortion. This bit shift can be
seen electronically when you read a data stream from a diskette. Data pulses which are
recorded close together when
read back, appear to spread apart. Precompensation advances or retards the data pulses as
they are written so the pulses are properly spaced when read back off the diskette.
All Heath/Zenith 5-1/4", 48 tpi, floppy disk drives require 120 ns of precompensation
on tracks greater than 23. Also, all Heath/ Zenith 8" and 5-1/4" 96 tpi drives
require 120 ns of precompensation
on tracks greater than 43.
Usually, two values of precompensation are needed: one for 5.25" drives and one for
8" drives. Accordingly, there are two precompensation adjustments on the Disk
Controller Card. Potentiometer R3
(PRECMP1) is used to set the lower value of precompensation and potentiometer R4 (PRECMP2)
is used to set the higher value of precompensation. Pictorial 1 shows the locations of
these potentiometers.