HP 7925D Service Manual page 82

Troubleshooting
CONTROL/
INDICATOR
Table 4-2. Disc Service Unit (DSU) Functions(Continued)
FUNCTION
7925
Function No.8 - Manual Mode (Continued)
Control Bits
Command
Address Unit
(ADU) - 1010
Clear Status
(CLS)-1110
Seek
(SK) - 1000
Set Offset
(SOF) - 1101
CO thru C2
co
CO thru C9
CO thru C5
Selects identity of drive to be enabled for
communication with DSU. (The identity of
the drive is the number selected on the
UNIT SELECT switch on the drive operator
panel.)
Clears three Attention flip-flops in drive.
This deactivates First Status signal.
Note: If CO and C1 are both selected, the
Attention flip-flops and the First
Status flip-flop are cleared.
Selects cylinder address to which heads
are to seek.
Selects offset magnitude in 63 increments
of 12.5 microinches each.
C7 Selects direction (+ or -) of offset.
Transmit Sector
(XMS) - 1100
CO thru C5 Selects sector address to be stored in drive
Sector Address register.
CO thru C15 LED
indicators
4-8
a. Indicates the state of the control bus bits selected by the lower band of 16 toggle
switches when anyone of the preceding six commands is selected.
b. Indicates the status of the drive when anyone of the following commands is
selected:
Read (READ) - 0000
Write (WRITE) - 0001
Request Status (RQS) - 0010
Coding for the
LED~s
is as foiiows. With the exception of Co (AeRY), a
lighted LED indicates that the corresponding signal is active. CO, when lighted,
indicates that signal ACRY is inactive.
CO - ACRY (Access Ready)
C1 - DRDY (Drive Ready)
C2 - Illegal head selected, illegal sector selected, or seek check
C3 - First Status
C4 - FLT (Fault)
C5 - Format
C6 - READ Only
C7 - ATT (Attention)
C8 - SC (Sector Compare)
C9 - High }
C9 on and C10 on, drive
=
7925
C10 - Drive Type
C11 through C15 - Not used