Spindle Rotation System; Spindle Logic Initialization; Door Control Logic; Run Spindle Command Logic - HP 7925D Service Manual

Theory of Operation
7925
and settled over any legal cylinder, the ACRY attention
flip-flop will be set by the leading edge of ACRY. If a seek
operation to the same cylinder address is attempted,
ACRY will remain active because the heads will not have
moved, but CYL will momentarily go inactive (CYL
=
0)
as the first seek command is dropped and then it will
return active (CYL
=
1) as the second seek command is
decoded. When this occurs, the ACRY attention flip-flop
will be direct-set by the leading edge of CYL. In both cases
(either a seek operation to a different cylinder address or
to the same cylinder address) when the ACRY attention
flip-flop is set, the controller is notified that a legal seek
operation has been completed (status bit 0
=
0 and status
bit 7
= 1).
Once the power supplies reach their proper operating level
(PSF
=
1),
SPEN will become active (SPEN
=
1) if en-
coder PCA-A10 interlock is not open. The speed down
detector will then detect that the spindle motor is stopped
and it will direct-set the speed down latch. Setting the
speed down latch causes SPD to become active (SPD
=
0).
1-27. DOOR CONTROL LOGIC. The door unlock
solenoid will be energized when the speed-down latch is
set, the carriage is retracted, the RUN/STOP switch is set
to STOP, and the power supplies are operating. When the
solenoid is energized, the pack chamber door will be un-
latched permitting access to the pack chamber and the
DOOR UNLOCKED lamp will light. A disc pack can now
be installed.
If a seek operation to an illegal cylinder is attempted, the
ACRY attention flip-flop will be inhibited from being set
because CYL will be held inactive (CYL
=
0), and instead
the SEEK e ICA flip-flop will be set as soon as the strobe
signal goes inactive (status bit 2
=
1 and status bit 7
=
1).
This will notify the controller of the illegal seek request.
If the RET signal becomes active (RET
=
1) for any reason,
the heads will be retracted and the drive ready flip-flop, on
drive control PCA-A4, will be reset. This will cause the
retract attention flip-flop to be set by the leading edge of
DRDY (status bit 1
=
0 and status bit 7
=
1). This will
notify the controller of the retracted condition of the
heads.
1-26. SPINDLE LOGIC INITIALIZATION. Dur-
ing the power-up sequence, PSF will momentarily become
active (PSF
=
0) because the power supplies have not yet
reached their full operating level. This will momentarily
hold the door unlocked solenoid de-energized which pre-
vents access to the pack chamber. In addition, it will cause
SPS to become active (SPS
=
0) which will reset both
current limit latches, direct-set the reverse direction de-
tector, and clock the speed down latch clear.
The spindle rotation system (see figure 4-25) consists of
circuits on drive control PCA-A4, spindle logic PCA-AS,
power and motor regulator (PMR) PCA-A9, and encoder
PCA-A10. Further, it includes such mechanical as-
semblies as the spindle motor, pack detector, and pack
loading assembly door lock mechanism. Communication
between drive control PCA-A4 and the rest of the circuitry
occurs via motherboard PCA-A7, while the remainder of
the communication occurs via the main harness. The
primary purpose of the spindle rotation system is to pro-
vide power to the spindle motor and to maintain its opera-
tional speed at 2700 revolutions per minute. In addition, it
operates the pack chamber door lock mechanism. Included
in the following are discussions relative to spindle logic
initiatization; the pack chamber door control, run spindle
command, and spindle motor phase encoding and decod-
ing, speed control and speed up detection, current regula-
tion, dynamic braking, speed down detection, overcurrent
protection, and overvoltage protection.
1-29. PHASE ENCODING AND DECODING. The
spindle motor is a brushless dc motor with two sets of
phase windings. Power is applied to each winding in a
prescribed sequence from the +36 and -36 volt supplies
through four current switches. Two switches are provided
for each phase winding because current is required to flow
through the winding in both a positive and negative direc-
tion. Each switch is activated three times during any
given revolution of the motor. It is the relative position of
the rotor with respect to the windings that determines
which switch to activate. Rotor position and motor speed
are derived by the phase encoder, from the encoder PCA.
This command will reset the speed down latch and the
reverse direction detector, and cause an encoder pulse to
be generated. The encoder pulse will clock the initial phas-
ing information from the phase encoder into the phase A
and phase B flip-flops.
With a pack installed and the pack chamber door closed,
the RUN/STOP switch can be set to RUN. Setting this
switch to RUN, sets the run/stop flip-flop. This will gener-
ate both a destructive and a non-destructive preset to
initialize the rest of the disc drive circuitry (refer to para-
graph 1-49). With STOP inactive (STOP
=
0), the door
unlock solenoid will be de-energized to again latch the
pack chamber door and the DOOR UNLOCKED lamp will
extinguish.
The phase encoder circuitry consists of an encoder disc,
which is fastened to the bottom of the spindle motor shaft,
and encoder PCA-A10. The encoder disc is a thin metal
disc with three 60-degree slots spaced 60 degrees apart.
Encoder PCA-A10 consists of two identical circuits, one for
phase A and the other for phase B. Each circuit is com-
prised of a light-emitting diode (LED), a phototransistor,
and an amplifier/inverter stage. The PCA is attached to
1-28. RUN SPINDLE COMMAND LOGIC. Once a
pack is in place (PIP
=
1), the pack chamber door is locked
(DL
=
1), the carriage is fully retracted from the pack
chamber (CRB
=
1), no interlock fault (lLF
=
0) or time-
out fault (TOF
=
0) exists, the run/stop flip-flop is set
(RUN
=
1),
and the run spindle flip-flop will be set to
generate the run spindle command (RS
=
0).
SPINDLE ROTATION SYSTEM
1-25.
1-12