Re: Connector P2 on 2040/4040 mainboard?

I've had a look at this a while ago.

If you modify a SA400 drive (or any other drive) then the interface
would be locked to that specific drive.

Although it would be slightly more complicated, the interface would be
much more universal if it did convert the Commodore "bit 0 and 1"
stepper motor signals to the regular shugart compatible step/dir
signals.

That way you could use any PC style disk drive, including for example
3.5" 1.44M drives, which would make it super easy to source media
(although 5.25" media isn't that hard to find, it's far harder and more
expensive than 3.5" HD disks) and for the 8050/8250/8250LP the disks
would also physically be compatible with other drives making it easier
to for example read/write disks with a cryoflux or similar.

A cosmetic problem with some kind of universal interface board is that
you would want all connected drives being enabled all the time.
Otherwise the digital board can't make the stepper move on one drive
while the other drive is reading/writing. Not sure if the digital board
ever does that, but it seems like a good idea to be totally compatible.
The result is that each connected drive needs to have it's own 34-pin
connector on the interface, and the LED on each connected drive will
stay on constantly or could be gated by the motor signal, which might
not reflect what the LED drive signal from the digital board tries to
signal.

As I see it, the only slightly tricky part about decoding the stepper
drive signals to step/direction is that you want to avoid glitches in
the signals. Perhaps add some circuit that is triggered by any change
and has a delay waiting some microseconds before considering the
signals stable, and then act upon them.

Any reasonable drive of the stepper drive signals would be either the
sequence 00,01,10,11,00,01,10,11 or 00,11,10,01,00,11,10,01. For each
off the four possible states of the control signals, there are only two
valid changes (one up or one down) so the invalid change (+/- two) can
be ignored. You might be able to decode this using standard 74xx/40xx
IC's but it seems simpler to use either a small eprom or programmable
logic. You could also most likely do this with a microcontroller as
they surely are fast enough to act upon signals intended to drive a
(relatively slow) stepper motor.

Btw if you or anyone else consider making some kind of universal
interface, it might be a good idea to also have the ability to connect
the regular Commodore analogue board to make it possible to combine one
working Commodore drive with another Shugart/PC compatible drive.

It might also be a good idea to consider making a board that can do the
reverse, i.e. making it possible to connect the Commodore analogue
board to a regular Shugart/PC compatible interface, making it possible
to use Kryoflux or similar stuff with the non-standard 100 TPI drives
used in the 8050/8250/8250LP/SFD1001 drives.

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