Conditions - HP 7925D Service Manual

7925
Table A-2. Operation Control Command Signals
Appendix A
MNEMONIC SIGNAL
ACTION
CLA
Clear Attention Resets Attention flip-flop.
CLS Clear First Status Resets First Status flip-flop.
CPS Controller Preset
Resets controller, together with Head, Sector, and Fault registers. Also
initiates self-test routine.
RED
Read One Sector Sector addressed by Head and Sector registers is read onto HP-IB.
RCL
Recalibrate Heads seek to cylinder O. Cylinder 0 is used as a reference. Correct location is
found by counting tracks from cylinder O.
SK Seek
Heads seek to target cylinder address, provided it is a legal address (0 - 822).
SOF Set Offset
Controller supplies, on control bus, amount and direction of head offset in 63
increments of 25 microinches each. Offset is stored in Offset register and heads
are offset as required.
WRT Write One Sector Data supplied by HP-IB is written into sector addressed by Head and Sector
registers.
REQUEST STATUS command is received, the controller
will transfer several bytes of data concerning the disc
drive and controller to the HP-IB. One byte is an encoded
word representing the status of the controller itself.
Another byte contains the drive type. The controller reads
this value, set by the absence of jumpers in sockets W362
and W363 on microprocessor PCA-A2, from the Drive Type
register. (The location of jumpers W362 and W363 on
PCA-A2 is shown in figure A-16.) The HP 7925H is type 3.
The third status byte comes from the Status register and
reflects conditions in the drive external to the controller.
Table A-3 lists the status byte bit assignments and each
bit is discussed in the following paragraphs.
Table A-3. Status Word Bit Assignments
BIT
STATUS
CONDITION
1
Access Not Ready
2 Drive Not Ready
3 Seek Check
4
First Status
5 Drive Fault
6 Format
7
Read Only
8
Attention
A-23. Access Not Ready. The access not ready
status bit will be active (status bit 1
=
1) whenever the
heads are not positioned over a valid track as determined
by the information on the servo surface of the disc.
A-24. Drive Not Ready. The drive not ready status
bit will be active (status bit 2
=
1) whenever the heads are
unloaded or a drive fault has occurred.
A-25. Seek Check. The seek check status bit will be
active (status bit 3
=
1) whenever one or more of the
following conditions exists:
a. An illegal cylinder address has been sent to the drive
via a SEEK command or during address verification.
b. An illegal head and/or sector address has been sent to
the controller via a SEEK, ADDRESS RECORD, or
COLD LOAD READ command.
An illegal head or sector is not accepted by the controller,
that is, the controller retains the previous head and/or
sector information. An illegal cylinder is accepted by the
controller without error indication, and a subsequent RE-
QUEST DISC ADDRESS command will return this ad-
dress. If the illegal cylinder address is sent to the disc
drive, the heads do not move and a Status-2 error (seek
check) is generated. The controller uses the DRV TYP
field to determine the legality of heads and sectors. The
disc drive itself determines whether the cylinder address
is legal. .
A-26. First Status. The first status status bit will be
active (status bit 4 = 1) when the heads are loaded to
identify this event to the user. The controller makes no
use of this bit. The controller clears the first status bit
after sending it to the channel.
A-27. Drive Fault. The drive fault status bit will be
active (status bit 5
=
1) and the DRIVE FAULT lamp will
be lit 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.
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.
A-II