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2.1.15 Write Safety
Data Unsafe Conditions
Circuits in the disk drive protect data from being
destroyed in the disk drive or the attachment. The
unsafe conditions that can occur are:
1.
2.
3.
4.
5.
6.
7.
Write selected and no write transitions
detected.
Write current source on but write not
selected.
Write selected and more than one or no
heads selected.
Write selected and off track detected.
Write selected and disk not synchronized
with attachment.
An open card interlock circuit.
Disk drive going not ready while writing.
When any of the preceding unsafe conditions
occur, write current is inhibited, accessing is inhib-
ited, and the heads are deselected. A data unsafe
line signals the attachment of the condition. A
recalibrate operation is required to bring the disk
drive to ready after resetting data unsafe. How-
ever, if a data unsafe condition cannot be reset, the
disk drive cannot seek or recalibrate. In this case,
if power is dropped, the actuator retracts.
File Ready
The disk drive either fails to go ready or goes not
ready after power up for any of the following
reasons:
1.
Interlock circuitry failure.
2.
Electrical failure in motor brake.
3.
Disk speed below 1,100 rpm.
4.
Ac power failure.
5.
Data unsafe condition.
Disk Speed
If the disk speed falls to 1,800 rpm ± 700 because
of motor failure or belt failure, the disk drive goes
not ready. The actuator then retracts and holds at
the inner stop until the disk stops. A magnetic
catch holds the actuator at the inner stop when
the retract capacitor is fully discharged after
power off.
Power Up
During power up, the actuator is held against the
inner stop until the disk is up to speed. This
ensures:
1.
2.
That the disk and control circuitry can
synchronize.
That the heads are flying before they move
out of the landing zone.
When the disk is up to speed, and a 32 second
timeout elapses, the actuator seeks home (track 0).
Ready is then indicated in the attachment.
Disk Drive
2-7
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