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.
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.
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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.
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 There was even and ANSI standard for the interface, but that got superceded by industry practice (ie, it was ignored).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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
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