Disc Service Unit (Dsu) Functions - HP 7925D Service Manual

Troubleshooting
Table 4-2. Disc Service Unit (DSU) Functions
7925
CONTROLI
INDICATOR
FUNCTION switch
START (STROBE)
pushbutton
STOP pushbutton
Upper bank of 10
toggle switches
(1 through 512)
Lower bank of 10
toggle switches
(1 through 512)
DELAY control
3-digit display
FUNCTION switch
START (STROBE)
pushbutton
STOP pushbutton
Lower bank of 9
toggle switches
(1 through 256)
DELAY control
3-digit display
FUNCTION switch
START (STROBE)
pushbutton
FUNCTION
Function No.1 - Alternate Seek
Selects automatic Alternate Seek function (position 1).
Starts operation of Alternate Seek function. Heads first seek to cylinder 0, then to
the cylinder address selected on the upper bank of ten toggle switches, and then
alternately between this address and the cylinder address selected on the lower
bank of ten toggle switches. If either selected address is an illegal one (greater than
822), the heads seek to the legal address and remain there. If both addresses are
illegal, only the seek to 0 (zero) is performed.
Stops operation of Alternate Seek function.
Selects cylinder address to which heads seek after leaving cylinder O.
Selects cylinder address to which heads seek after leaving cylinder address
selected by upper bank of 10 toggle switches.
Selects time interval between seeks.
Indicates time interval for seek. Readout is in milliseconds.
Function No. 2 - Incremental Seek
Selects automatic Incremental Seek function (position 2).
Starts operation of Incremental Seek function. Heads first seek to cylinder 0 and
then to next address. Next address is determined by adding the numbers selected
by the lowest ten (1 through 512) switches on the lower bank of toggle switches.
Incremental seeking of the heads to the next address continues until a next address
greater than 822 is reached. When this occurs, the programmed next address
number is subtracted from the preceding valid next address (822 or less), causing
decremental seeking to the next address until cylinder 0 is reached. The heads
continue this incremental and decremental seek action until the STOP pushbutton
is pressed.
Stops operation of Incremental Seek function.
Selects amount by which current cylinder address is incremented (or decremented)
for next seek.
Selects time interval between seeks.
Indicates time for seek. Readout is in milliseconds.
Function No.3 - Random Seek
Selects automatic Random Seek function (position 3).
Starts operation of Random Seek function. Heads first seek to cylinder 0 and then
to cylinder addresses generated by the DSU in a pseudo-random sequence.
Note: On functions 1 through
3,
head 0 and sector 0 are selected before the initial seek to 0 (zero).
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