8300
(3)
Load Heads (LLHFF), a flip-flop output state used for controlling the position
control logic and loading and unloading the heads.
(4)
Emergency Unload (LEUFF), a flip-flop output state used to indicate that
an
emergency unload condition has started or presently exists.
(5)
Load or Purge Not (NLLPNG), the output
of
combinational logic within the
Startl
Stop Control; this combinational logic decodes the states
of
two of the major
state storage flip-flops, Purge Cycle and Load Heads. NLLPNG is used for
initializing the position
limit
monitor contained within the Position Control Logic.
(6)
Brush Motor Enable (NLBMEG), controls the power to the brush motor in top load
models
of
the disk drive for operating the disk cleaning brushes.
(7)
Brake Cycle Enable (NLBCEG), the control signal which determines when the
braking current is applied
to
the disk drive motor.
(8)
Lock Cartridge Mechanism (LLCMG), controls the solenoid drivers
on
the Servo
PCBA
and is the signal which determines when the cartridge mechanism is locked
or unlocked.
(9)
Emergency Unload Enable (LEUEG), controls the emergency unload relay driver
on
the Servo PCBA;
this
relay driver, in turn, actuates the emergency unload relay
as
commanded by the Emergency Unload Enable signal.
The
output signals from the Start/Stop Control circuitry described in
(1)
through
(5)
are
used
on
the Logic PCBA
for
specific control functions. The signals described in
(6)
through
(9)
are fed directly to the Servo PCBA.
Three signals for driving the operator control panel lamps are generated
by
the Condition
Indication portion
of
the Start/Stop Control logic. These signals
are
Safe Lamp Drive
(NLSLDT),
Run
Lamp Drive (NLRXDn, and the Ready Lamp Drive (NLRLDT).
The
SAFE
lamp is used to indicate when
it
is safe for the operator to remove or insert a cartridge into
the disk drive; the
RUN
lamp is used to indicate when a machine is executing a start
sequence,
or
the disk is running. Illumination of the
READY
lamp indicates that the disk
drive has achieved the Ready condition.
Other signals generated by the Condition Indication logic are: Ready (LRXXG), Selected
And
Ready
(LSARG), Delayed Ready Condition (LDRCG): The Ready signal is the output
of combinational logic and is the combination
of
several flip-flop states within the
Start/Stop Contol. The Selected and
Ready
signal is the Ready signal combined with the
Selected signal from the
unit
select logic. The Delayed Ready condition is the
Ready
signal passed through a delay network. Ready, Selected And Ready, and Delayed
Ready
Condition signals are used in other parts of the Function Control Logic as well
as
enabling
certain portions
of
the Position Control Logic and the Sector Electronics Logic.
4.7.2.2 Minor Control Functions
The
minor functions discussed in the following paragraphs
are
contained within the Disk
Drive Function Control logic block shown in Figure 1-4.
Due
to the nature of these minor
control functions, no attempt is made to relate these functions to a simplified block
diagram. The circuitry which performs these logic functions is contained
on
sheet three of
the Logic
PCBA schematic.
The
Select and Control Logic consists
of
a holding register and associated control gates
for processing the Platter and Head
Select lines, the Track Offset Plus, and Track Offset
Minus lines. Also included is the Write Double Frequency Data Re-transmitter which acts
4-20
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