
Set Sector
Description:
This command resets orientation in the control unit. The Set Sector
command transfers a 1-byte relative angular track position to the control unit. The
sector number causes the logical volume to position to a specific sector before
starting the next command. If the sector number is zero, the next command starts
with the logical volume in a position immediately before index. A sector value of
X
'
FF
'
specifies that sector positioning is not to be done before starting the next
command.
Note:
Record orientation is not assured. A search command must follow this
command to verify that the logical volume is at a specific record.
The control unit presents channel end and device end. No further action occurs
until the control unit receives a command requiring track orientation. At that time,
all cache directory searches and/or access actions occur before orientation.
If more than one Set Sector command is saved before orientation is required, only
the last sector number received is used. Previous values are discarded. Any
sector value stored and not used at normal or unit check completion of command
chaining is discarded.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is in the domain of a Locate Record or Locate Record
Extended.
This command is not preceded in the command chain by a command that
specifies (or implies) (CCHH) parameters; Seek, Seek Cylinder, Locate Record,
or Read IPL command.
The control unit requests a single byte sector number from the channel. If the
channel does not send a data byte, the command is rejected with unit check status.
The sense data contains command reject with format 0, message 3.
The sector number must be valid for the logical volume. If the sector number is not
valid, the command is rejected with unit check status. The sense data contains
command reject with format 0, message 4. See Appendix A, "Device
Characteristics" on page A-1 for the valid sector numbers for a specific emulated
device type.
Ending Status:
See the command description.
Hex Code
Data Address
Count
23
The main storage location of the sector byte.
1
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