Search ID Equal
Description:
The Search Identifier (ID) Equal command causes the control unit to
request a 5-byte record ID (CCHHR) from the channel and compare that data with
the 5-byte count area ID read from cache. If the channel sends fewer than 5 bytes,
the control unit compares the data received with an equal number of bytes of the
record ID.
If the control unit is oriented to home address when it receives the command, it
reads the record zero count area. If the control unit is not oriented to home
address, it is oriented to the next count area and reads that area. If end-of-track is
detected before a count area is found, the operation continues according to the
state of the multitrack bit (bit 0) in the CCW:
If the multitrack bit is ‘0’, the control unit is oriented to home address and reads
the record zero count area on the same track. If the track does not have a R0,
the command is terminated with unit check status. The sense data includes No
Record Found.
If the multitrack bit is ‘1’, the control unit advances to the next track and
continues to a record zero count area, or until the operation is terminated with
an end-of-cylinder exception. See “Operations Outside the Domain of a Locate
Record or Locate Record Extended” on page 4-3.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if this command is:
Not preceded in the command chain by a Seek, Seek Cylinder, Locate Record,
Locate Record Extended, or Read IPL command.
In the domain of a Locate Record or Locate Record Extended
Ending Status:
The control unit presents channel end and device end status
when the compare operation is complete. If the search argument compares equal
to the corresponding bytes in the record ID, status modifier is included in ending
status. When the command completes, the control unit is oriented to the count
area that it read.
Hex Code
Data Address
Count
31
Multitrack
B1
The main storage location for the
record identifier; cylinder (CC),
head number (HH), and record
(R).
5
Chapter 4. Command Descriptions
4-79
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