Seek
Description:
The Seek command transfers the track address to the control unit.
The format of the seek address parameter is (00CCHH), where (00) is 2 bytes of
binary zeros and (CCHH) is a 4-byte track address.
The control unit saves the seek address to do a cache directory search or to
position the actuator at a later time.
Chaining and Restrictions:
This command is not valid in the domain of a Locate
Record or Locate Record Extended. If the Seek command is in the domain of a
Locate Record or Locate Record Extended, it is rejected with unit check status.
The sense data contains command reject with format 0, message 2.
If the file mask inhibits seek commands (bits 3 and 4 are not ‘00’), this command is
terminated with unit check status. The sense data includes File Protected.
The control unit requests a 6-byte set of address parameters from the channel. If
the channel sends fewer than 6 bytes, the command is rejected with unit check
status. The sense data contains command reject with format 0, message 3.
The track address is checked for validity for the current access authorization and
the logical volume type. (See Appendix A, "Device Characteristics" on page A-1.)
If the seek address parameter is not valid, the command is rejected with unit check
status. The sense data contains command reject with format 0, message 4.
If a Seek command is preceded in the channel program by a Define Extent
command, and the seek address is not in the defined extent, the command is
terminated with unit check status. The sense data includes File Protected.
Ending Status:
After the control unit receives a valid parameter and checks the
cache directory to determine if the track is in cache, it saves the track address and
presents channel end and device end status.
The track accessing operation is deferred as described under “Seek Operations” on
page 4-46.
Hex Code
Data Address
Count
07
The main storage location of the seek address.
6
Chapter 4. Command Descriptions
4-47
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