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In article <880721-140208-4503@Xerox> "Robert_L._White.ESXC15"@XEROX.COM writes:
>Hi, I just FTP'ed the schematic for the step doubler.
>Program 40_80_tr.pi3
>I have some questions though.
>	1) what exactly does this do? i.e. does it double the step pulse from
>		one pulse to two pulses, or lenghten the step pulse.

To make a 80-track drive read 40-track-PClone disks, it produces 2 step
impulses from one. 

>
>	2) must you use a hi density 5.25 (1.2 meg) to use the 80 track 		feature?  I
>didnt think the standard 5.25 that an IBM uses 		would do 80 tracks.

There are 80-track-dd-drives. The "standard IBM" uses 40-track-dd like
Teac 55B. The Teac 55F is exactly the same as the 55B, except for the
head (the 80-track type writes smaller tracks) and one resistor (for
internal doblestepping).
If You connect an 80 track drive (beware of the pullup resistors and so
on) *without* a step doubler, it "looks" like an 3.5" to the ST; the
interface Sony used for their first 3.5" drives is the 5.25"-Shugart
BUS.
The HD drives the AT uses are 8"-look alikes (to the controller chip);
they were chosen because of their speed, which is 500 kbit per second
(versus 250 from a 5.25" drive/interface). The extra capacity was a neat
bonus. 
Most HD drives can "fallback" to 80 track double density, for
unformatted 1 megabytes or 720 KBytes with IBM-format. The AT software
(BIOS) does not handle this format. With double density the AT-Bioses
use double stepping to read 360 Kbyte (40 track) disks.
>
>
>I currently have a 5.25 hooked up, but have several problems. I have changed the
>memory locations required to make the step pulse 6ms but still I have problems.
>
>The problems are:
>		1) I cannot format the 5.25 under pc-ditto 40 track, it fails.
>			The drive seems to do a lot of stepping.
>		2) I have written a "c" program to format for 40 tracks, and 			that works
>with no problems (no errors returned), 			except that I get allot of disk errors
Maybe that PCDitto does another doublestep (quadrostep alltogether) when
formatting 40 tracks. Try do disable you step doubler.
Or PCDitto does not use the TOS-step rate code ans steps with 3 msec.
Ask the authors of PCDitto.

I hops this helps a little

hase
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