HP 7925D Service Manual page 194

Appendix A
A-28. Format. The format status bit will be active
(status bit 6
=
1) whenever the FORMAT switch on the
operator control panel is set to the format position (.).
A-29. Read Only. The read only status bit will be
active (status bit 7
=
1) and the read only lamp will be lit
whenever the READ ONLY switch on the operator control
panel is set to the protected position (.) thereby inhibiting
any write operations.
A-30. Attention. The attention status bit will be ac-
tive (status bit 8
=
1) at the completion of a SEEK or a
RECALIBRATE, or when the heads load or unload. The
attention status bit is cleared by the controller (not re-
ported to the channel) except when the heads unload due
to a drive fault.
A-31. ATTENTION LOGIC. There are two atten-
tion flip-flops in each disc drive which are used to control
the state of the attention bit (status bit 8). This status bit,
in conjunction with other status bits, is used to notify the
controller when the disc drive has performed certain oper-
ations. The ACRY and retract attention flip-flops are lo-
cated on drive control PCA-A4. Both flip-flops are initially
reset by CLA (via NDPS) when power is first applied or
the RUN/STOP switch is set to RUN. When reset, these
flip-flops cause the attention bit to be inactive (status bit
8
=
0).
Every time the RUN/STOP switch is set to RUN and the
disc pack has come up to speed, a seek home operation will
be initiated. When the heads are correctly positioned over
cylinder 0, the ACRY attention flip-flop will be set by the
leading edge of ACRY. This will notify the controller that
the seek home operation has been completed.
During normal seek operations, the ACRY and retract
attention flip-flops are reset once the heads leave the
cylinder over which they were settled. Once the heads are
correctly positioned 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 drop-
ped 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.
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 This will notify the controller of the retracted con-
dition of the heads.
A-12
7925
A-32. SPINDLE ROTATION SYSTEM
The spindle rotation system (see figure A-17) consists of
circuits on drive control PCA-A4, spindle logic PCA-A8,
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
chamber 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
initialization; 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.
A-33. 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.
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).
A-34. 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.
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 1-58). 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.
A-35. 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