Disk II Stepper Phase Motor?

[vantune@fraser.sfu.ca (Joseph Van Tunen)]

How are the four stepper motor phase soft switches (5.25" disk drives)
used to move the disk arm inward and outward over the tracks
($C0E0..$C0E7)? How is the arm moved 1, 1/2, (and 1/4) track at a
time?  (Copy II Plus has options for doing 1/4 and 1/2 tracks). What
timing is required? Not all drives can step a 1/4 of a track, right?
But the timing should remain the same no matter what kind of drive, I
guess...  I have the Beneath Apple DOS book (c1981) which doesn't
explain it all. It does mention where in the DOS 3.3 code (RWTS) the
seek routine is but the Disk II has 70 phases, 1 track every second
phase, which allows only half tracks. What about 1/4 tracks (is there
such a thing)?  Are there drives with more than 80 phases? I could
disassemble the Copy II Plus code and find how it seeks tracks, but
I'ld rather not. Does ProDOS have commands for seeking tracks (1/4 and
1/2 also)?

Sample assembly code would be nice..

-------------------------------------------------------------------------------
-- Joe van Tunen                                       (e-mail: vantune@sfu.ca)
-- Fort Langley, B.C., Canada.

-- Undergraduate, Simon Fraser University
-- Burnaby, B.C., Canada.