retracting the heads during a normal unload when either a Write or
an
Erase command
from the
110
interface is occurring.
Correct insertion of the cartridge is detected by two switches
in
top load machines, and by
one switch
in
front load machines. This interlock prevents starting the disk drive when the
cartridge is not inserted.
In
top load machines the parked position of the cleaning brushes
is interlocked by a switch for purposes of determining that the brush cleaning cycle has
been
satisfactorily completed.
The Power
Clear signal (SPCSA) from the Servo PCBA signals when
an
unacceptable
power supply condition is sensed. The
SPCSA signal is provided
to
the Start/ Stop Control
logic
as
well
as
to the Read/Write PCBA. Also supplied from the Servo PCBA is the Heads
Retracted signal
(SHRXG) which is used by the Interlock Control to ensure that the disk
does not stop rotating unless the heads are retracted.
The
purpose
of
the Emergency Unload Logic is
to
begin
an
emergency unload operation
when commanded externally, or when this logic detects certain
fault situations which
require emergency unloading of the heads from the storage surface.
One of these fault
conditions is the Position Transducer Failure
(SPTFG) condition. This condition is
detected
on
the Servo PCBA and is provided
to
the Emergency Unload Logic should a
failure occur in the position transducer. Another signal, the Write Emergency Condition
(RWECG) is generated
on
the Read/Write PCBA should a write emergency condition
be
detected. Additionally, the Activate Emergency Unload (IAEUR)
I/O
interface line is
provided for commanding emergency unloads from the
I/O
interface .
.
All other emergency unload conditions are detected by logic circuitry
on
the Logic PCBA.
Three of these emergency conditions are detected within the
Start/Stop Control
arrangement by the Emergency Unload Logic. The signals utilized are: Not Position Mode
(NLPMXG),
Speed Out of Tolerance (LSOTF), and
an
internal signal within the Start/Stop
Control
logic. This internal signal is generated by the Interlock Control Logic from the
state of the Brushes Parked switch and is not shown on the block diagram. The Not
Position Mode (NLPMXG) logic state is tested by the Emergency Unload Logic to
determine
if
the heads
have
properly loaded during a start sequence. Speed Out of
Tolerance
(LSOTF) is tested during the start sequence to determine
if
the disks
have
reached the proper speed prior
to
loading the heads. The internally generated signal from
the brushes parked switch is tested to determine that the brush cleaning cycle has
been
correctly completed.
Elsewhere within the logic, three signals are generated upon detection
of
a specific fault
condition and are provided to the Emergency Unload Logic. These
Signals are Not Position
Limit
Error (NLPLEG), Not Disk Speed Error (NLDSEG), and Not Seek Time Error
(NLSTEG). The Not Position
limit
Error signal commands emergency unload when the
positioner exceeds its legal range of
travel. The Not Disk Speed Error signal commands
an
emergency unload when a disk speed error is detected after the system achieves the Ready
condition. The Not
Seek Time Error Signal commands
an
emergency unload when the time
for a seek exceeds the
allowable maximum.
The major function control output signals from the
Start / Stop Control are:
(1)
Start Drive Motor (NLSDMG), a pulse used for initializing the spindle speed
control logic.
(2)
Purge Cycle (LPCFF), a flip-flop output state used for controlling the disk
speed during the purge cycle.
4-19
8300
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