Attention Logic - HP 7925D Service Manual

7925
1-15. Drive Ready. The drive ready status bit will
be active (status bit 1
=
1) and the DRIVE READY lamp
will light whenever the heads are positioned over the data
area of the disc pack (cylinders 0 through 822).
1-16. Seek Check. The seek check status bit will be
active (status bit 2
=
1) whenever one or more of the
following conditions exists:
a. The controller has placed an illegal cylinder address
(cylinder address> 822) on the control bus with a
SEEK command on the tag bus. This condition will
also cause the attention bit to be active (status bit
7
=
1).
b. The controller has placed an illegal head address
(head address > 8) on the control bus with an ADR
command on the tag bus.
c. The controller has placed an illegal sector address
(sector address> 63) on the control bus with either an
ADR or XMS command on the tag bus.
d. The controller has attempted to command a seek op-
eration while the disc drive was in the process of
executing a previous SEEK command.
This bit can be cleared if a legal operation (SEEK, ADR, or
XMS) is performed to correct the error. The attention bit
can be selectively cleared by the controller if it issues a
CLS command on the tag bus with bit 0 active on the
control bus.
1-17. First Status. The first status, status bit will be
active (status bit 3
=
1) whenever the disc drive initially
loads the heads. This bit can be selectively cleared by the
controller if it issues a CLS command on the tag bus with
bit 1 active on the control bus.
1-18. Drive Fault. The drive fault status bit will be
active (status bit 4
=
1) and the DRIVE FAULT lamp will
light whenever the disc drive fault circuits detect either a
read/write, servo, or interlock fault condition. Non-
destructive read/write faults (W. AR or R. W) can be
cleared by the controller if it issues a CPS command on the
tag bus. Destructive read/write faults (W. AC, or
DC • W, or MH), servo faults (T, AGC, or CRB), or an
interlock fault (IL) cause the heads to unload. Operator
intervention will therefore be required.
1-19. Format. The format status bit will be active
(status bit 5
=
1) whenever the FORMAT switch on the
operator control panel is set to the format position (.).
1-20. Read Only. The read only status bit will be
active (status bit 6
=
1) and the READ ONLY lamp will
light whenever the READ ONLY switch on the operator
control panel is set to the protected position (.) thereby
inhibiting any write operations.
Theory of Operation
1-21. Attention. The attention status bit will be ac-
tive (status bit 7
=
1) whenever the disc drive:
a. Correctly positions the heads over cylinder 0 (initial
head load or RCL operation).
b. Retracts the heads under either normal or abnormal
(fault) circumstances.
c. Completes a seek operation to a legal cylinder address
(cylinder address ~ 822).
d. Is commanded to perform a seek operation to an il-
legal cylinder address (cylinder address> 822). This
condition will also cause the seek check status bit to
be active (status bit 2
=
1).
This bit can be selectively cleared by the controller if it
issues a CLS command on the tag bus with bit 0 active on
the control bus. Refer to paragraph 1-24 for more detailed
information regarding attention logic operation.
1-22. Sector Compare. The sector compare status
bit will be active (status bit 8
=
1) only during a read or
write operation for as long as the present sector equals the
addressed sector. This bit will be cleared whenever the end
of the addressed sector is reached or the READ or WRITE
command is dropped.
1-23. Drive Type. Status bits 9 and 10 enable the
controller to determine the type of disc drive, total number
of heads, and the number of sectors per track. The drive
type code for an HP 7925 Disc Drive is 11, therefore, bits 9
and 10 will always be active for this type of disc drive.
1-24. ATTENTION LOGIC. There are three atten-
tion flip-flops in each disc
dri~e
which are used to control
the state of the attention bit (status bit 7). 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, and the SEEK. ICA flip-
flop is located on I/O sector PCA-A2. All three 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 7
=
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 (status bit 0
=
0 and status bit
7
=
1). 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 (status bit 0
=
1 and
status bit 7
=
0). Once the heads are correctly positioned
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