stepper motor of floppy disk

[[email protected]]

Hello,

I want to control stepper motor of sony floppy disk. I know that here
is three pins on bus which are to control this motor. This is STEP
pin, DIRECTION pin and MOTOR pin. I know that DIRECTION pin have
influance just on direction of motor. MOTOR pin just starts/stops
motor ( start - high and stop - low signal ? where high ~ 4.5 V ) .
But I really don't know how I should control STEP pin. Can I assume
that when STEP is high then motor is stepping?
Or maybe then motor execute only one step?

I would be very glad if someone would like to explain me how it
works.

Wiktor

 

[Tim Wescott]

Hello,

I want to control stepper motor of sony floppy disk. I know that here
is three pins on bus which are to control this motor. This is STEP
pin, DIRECTION pin and MOTOR pin. I know that DIRECTION pin have
influance just on direction of motor. MOTOR pin just starts/stops
motor ( start - high and stop - low signal ? where high ~ 4.5 V ) .
But I really don't know how I should control STEP pin. Can I assume
that when STEP is high then motor is stepping?
Or maybe then motor execute only one step?

I would be very glad if someone would like to explain me how it
works.

Wiktor

Normal step/direction/enable functionality is that the enable (probably
MOTOR in your case) turns the driver on, direction controls the
direction, and step causes the motor to advance one step (or one
microstep if it's such a driver) for each rising (or sometimes falling)
edge on the step input.

So to get the motor to go someplace you need a square wave on the step
command.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[whit3rd]

I want to control stepper motor of sony floppy disk. I know that here
is three pins on bus which are to control this motor. This is STEP
pin, DIRECTION pin and MOTOR pin. I know that DIRECTION pin have
influance just on direction of motor. MOTOR pin just starts/stops
motor ( start - high and stop - low signal ? where high ~ 4.5 V ) .
But I really don't know how I should control STEP pin.

A floppy drive has two motors, one that rotates the spindle and drives
the disk , and another that positions the read/write head. It's
probable
that the MOTOR pin controls the spindle rotation (usually there's a
multiphase
AC motor for that) while the DIRECTION and STEP control the stepper
motor that (through a screw-drive) moves the read/write head.

Application notes on ICs for driving these motors might be
illuminating (BA6980 seems
to be the part number on the first Sony floppy drive I find). The
'step' command
in the drive interface is inherited from old 5.25" floppies, it might
drive any number
of steps on the actual motor interface after the control logic
interprets the command.
Steps are likely to occur on the high-to-low transition of the STEP
signal.

There's a bit of clucking from a disk drive at startup, when the step
motor is
moved to its end-of-travel; I'd expect another line on the interface
that reports the
end-of-travel condition after stepping.

 

[[email protected]]

A floppy drive has two motors, one that rotates the spindle and drives
the disk , and another that positions the read/write head. It's
probable
that the MOTOR pin controls the spindle rotation (usually there's a
multiphase
AC motor for that) while the DIRECTION and STEP control the stepper
motor that (through a screw-drive) moves the read/write head.

Application notes on ICs for driving these motors might be
illuminating (BA6980 seems
to be the part number on the first Sony floppy drive I find). The
'step' command
in the drive interface is inherited from old 5.25" floppies, it might
drive any number
of steps on the actual motor interface after the control logic
interprets the command.
Steps are likely to occur on the high-to-low transition of the STEP
signal.

There's a bit of clucking from a disk drive at startup, when the step
motor is
moved to its end-of-travel; I'd expect another line on the interface
that reports the
end-of-travel condition after stepping.

maybe the step pin need a impulse,at the rising edge or falling edge
of the impules.the the stepper motor can work

 

[Mark Zenier]

Hello,

I want to control stepper motor of sony floppy disk. I know that here
is three pins on bus which are to control this motor. This is STEP
pin, DIRECTION pin and MOTOR pin. I know that DIRECTION pin have
influance just on direction of motor. MOTOR pin just starts/stops
motor ( start - high and stop - low signal ? where high ~ 4.5 V ) .
But I really don't know how I should control STEP pin. Can I assume
that when STEP is high then motor is stepping?
Or maybe then motor execute only one step?

One step per pulse. See if you can find the datasheet for a floppy
disk controller chip. There was even and ANSI standard for the
interface, but that got superceded by industry practice (ie, it was
ignored).

I think newer disk drives will keep a count of the pulses so that
they can be sent at a much faster rate than the mechanics will move.
Older controllers had to set the rate at which the drive could step.
Really old drives were quite slow.

If you're driving the motor directly, this doesn't apply.

There are a couple of types of stepper motor used for floppy head
positioning.

If the motor shaft spins freely (disconnected from any circuity), it's a
Variable Reluctance stepper and usually has three motor windings. You get
it to rotate by driving one (or two) of the three windings at a time,
and the direction it goes depends on the sequence. Driving two windings
at the same time gives it more power. Either case (one or two windings
driven) have three possible drive combinations. They're indpendent of
the polarity of the drive signal. They can be thought as a special kind
of solenoid. These motors are usually cylindrical and used in drives
with a lead screw mechanism.

If the motor detents/cogs when you try to rotate it, it's a permanent
magnet stepper. They have two sets of windings and the polarity
(direction of current in the winding) matters. The two windings (often
split into four seperate connections) end up with eight different
combinations of positions. The buzzword here is Full Step, or Half
Step (where you always drive two windings at once with four possible
position sets). These are usually square (at least those used in 5 1/4
inch drives) and used a metal ribbon to connect the drive to the head.

(Anybody got the URL for Doug Jones' stepper motor web site?).

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[[email protected]]

Thanks for help!

Wiktor