27 Nov
2005
27 Nov
'05
1:45 a.m.
On 11/27/2005 at 12:03 AM ard at p850ug1.demon.co.uk wrote:
I think it's a combination of the stepper used (Molon LMS on the earlier
drives and Hansen Synchron on the later drives; both were 7.5 degree
models). Fairly large, so they probably could not have been stepped very
quickly. Nameplate rating on the Hansen is 12v 0.9a, so not power misers
either.
Micropolis
drives were 30 ms. track-to-track. I believe they used a
4-step
I am not disputing that the Micropolis drives were slow. What I am
questioning is whether that was solely due to the use of a leadscrew. Interesting, I've never seen a floppy drive with
buffered seeks, and
since there's no seek-complete pin on the interface connector, I don't
see how it could really work. Every floppy controller I've ever seen
sends the step pulses at a constant rate, which would have to be slow
enough for the worst case.
READY goes false while seeking. You can issue pulses as fast as you want
(I know the drive will take a pulse every 2 msec. and probably much
faster). In a way, this isn't all that different from the overlapped seek
capability of the 765 controller; you issue the seek and wait for READY to
go true (or SEEK COMPLETE to be set in the case of the 765) Whether or not
the drive has a disk inserted appears to be unimportant. You can issue
your read or write when READY goes true.
As I said, a very strange, probably expensive drive and a floppy
evolutionary dead end.
However, the Drivetec drives also use leadscrew positioning (2 of them) and
still manage to get a 3 msec. track-to-track seek time (or faster for long
seeks). But their steppers are tiny in comparison to the Micropolis units.
Their buffered seek uses pin 4 as a combination READY/SEEK COMPLETE
signal. Pin 2 true only tells you that a disk is in the drive and
spinning. The Drivetec also masks INDEX while seeking; I'm not sure about
the Micropolis, but it would make sense to do so.
OT: has anyone figured out how to format the 2.88MB or the 6.4 MB
diskettes on the Drivetec units?
Sure... I remember the Sanders dot matrix printers that
ramped up (and
down) the step rate of the carriage feed stepper and sent the printhead
pulses at just the right times to put the dots in the right places.
Are you certain that Sanders used a stepper for carriage positioning? If
they were like Diablo or any of the other high-speed printers, it was more
likely a DC motor with encoder. Steppers were just too slow, particularly
for bidirectional "smart" printing. IIRC, one of the engineers who worked
on the Diablo dot matrix printer (can't recall the model number, but it
used the Rockwell PPS-8 set) said that the whole business of accelerating
and decellerating a mass like a printhead made for some interesting
programming.
Paper feed, on the other hand, was almost certainly stepper-driven.
Cheers,
Chuck