Re: updated

From: Ruud Baltissen (
Date: 2001-08-31 13:35:19

Hallo Nicolas,

> > Knowing now that you used a former 360 KB drive means that for
> > a 360 KB floppy "1 track = 2 steps".
> Not really ;-) I used just the bare drive mech, without the stepper
> driver control.

That is what I assumed and therefor the above conclusion.

> I didn't do anything about the
> r/w head currents, it just works without any changes in my case.

The remark was made having an HD-drive in combination with a HD-floppy in

In the early days when I had a 8250 but no matching FD's, I used 48 TPI ones
with reasonable succes. I wonder if they can be used as well in a 1541/HD

> > - And what about skipping the analogue part of the 1541 and connecting
> > TTL-signals to the according shugartbus-pin?
> > - And to hook the diskcontroller/6522 directly to the shugartbus?
> > requires SW change)
> I don't see the difference between these two.

With the first point I meant that we only use the electronics of the 1541 to
steer the steppermotor. So at some point a TTL-signal is tapped from the
board to be fed to the shugartbus. And the read data is fed to the board at
another point (after disabling the original signal of course).

With the SW change I meant converting the outputs of PB0 and PB1 from
"direct driven phase" to "pulse/direction". But your idea using a circuit is
much better.

> First the stepper is set to track 1 and then the head
> bump is executed. After the bump sequence, the stepper register is
> still set to track 1.

Don't you mean track 0 ???

> While I could come up with a circuit that converts the phase
> output to the step/dir output, I will lose the direct relation
> between the phase and the r/w head position.

Correct. If you allow me to rephrase it: in a 1541 PB0 normally is (L) when
the head is placed above a valid track. With the mentioned circuit the
chance is 50/50 that PB0 is (H). But....

> it needs to make use of an optical
> track 0 sensor, which is not supported by the 1541.

My idea is to use this sensor in the hardware, not SW. The moment the head
is on track 0, the sensor disables any stepping pulse when the direction is
down, like when performing a "Bump". After the Bump the head is above track
0 and PB0/PB1 is alligned ie. PB0 = (L).

The only thing needed is a way to let the drive perform a bump after a
reset: 1) run a small program or 2) hack the ROM and use the 256 free bytes
at $C000/C0FF.

> With little changes in the drive firmware, it would be easy to interface
to a
> Shugart drive directly, but it would break compatibility with many
> copy protection schemes, and probably copy programs as well.

IMHO the above proposals don't break compatibility.

> .... we don't want to have yet another new disk format.

You're absolutely right. I completely forgot that the 1581 uses MFM, which
the 1541 isn't capable to handle.

  / __|__
 / /  |_/     Groetjes, Ruud
 \ \__|_\

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