Re: FB-354 drive incompatibility

From: Michał Pleban <>
Date: Sun, 24 Apr 2016 13:16:23 +0200
Message-ID: <>
Hello! wrote:

> A selected drive will drive this signal low whenever its internal "disk
> change" latch is set. This latch is set when the drive is first powered
> on, or whenever there is no diskette in the drive. To reset the latch,
> the system must select the drive and step the head. Of course, the latch
> will not reset if there is no diskette installed.

OK, so I understand that the latch sets when the disk is "removed".

So I see a solution which does not require the "click" at all. Assert
the /MOTOR signal. If there is a disk in the drive, the disk will spin
and the /RDY signal will be asserted after the motor spins. Then we know
there is the disk in the drive, so we can stop the motor. We can step
the head now so the latch is cleared.

If there is no disk, the motor will not spin [*] so the /RDY signal
never comes. That's how we know where is no disk.

So the trick here is to assert /MOTOR whenever the /CHG line is asserted
and with for the /RDY. Then when /CHG appears, it means the disk was
removed. When /RDY appears, it means that the disk is inserted and
/MOTOR can be deasserted. The only non-standard thing here is to step
the heads once when the disk is inserted - a MCU may be still required

[*] At least on the FB-354B mech I am playing with. The idea will not
work if the mech spins the motor without the disk inserted.


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Received on 2016-04-24 12:00:02

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