Re: //c external drive continuously running.

[dempson@actrix.gen.nz (David Empson)]

ianoid <ianoid@gmail.com> wrote:

> I have been testing out some of my Apple //c hardware, and I've come
> across an external drive for //c that behaves rather oddly. When I
> boot from the internal drive, the external drive runs continuously. I
> am actually able to access disks from the external drive, and even run
> programs from it. But no matter what happens, it just keeps on
> running. I can reset, and it just keeps running. Nothing seems to make
> a difference.
> 
> I have tried the same computer with 2 other external drives which
> operated normally.

The drive probably has a fault in the cable or on its analog board,
which makes it thinks the "select" line is permanently active. This will
keep the motor spinning but doesn't prevent access to the drive.

The soft-switches are designed to prevent two drive motors being enabled
at once (on the same slot) - the computer can turn the motor on and off,
and a separate signal selects between drives 1 and 2. These two signals
are combined to form enable lines which go to drive 1 and to drive 2,
which are on separate pins of the drive connector. (One drive is
internal in the IIc, so there is only one exposed drive enable signal on
the external connector.)

The power supply is only designed to cope with a single drive spinning
at a time, so having that drive running constantly is risking an
overload of the power supply.

In other Apple II models (with slots) that have multiple drive
controllers, the operating system is responsible for ensuring that only
one slot's "motor on" soft-switch is active at any time.

-- 
David Empson
dempson@actrix.gen.nz