The control unit uses the seek address and sector number parameters to start track
access. When track access is complete, the search operation specified by the
search argument and the orientation modifiers (byte 0, bits 0 and 1) is performed.
The Locate Record command must be followed by the number of read CCWs
needed to process the number of records specified by the count parameter. The
Read Multiple Count Key and Data, Read Track, and Read IPL commands are not
valid in the Locate Record domain. Any other sequence of read commands is
valid. If the Locate Record domain contains an invalid command sequence, the
invalid command is rejected with unit check status. The sense data contains
command reject with format 0, message 2.
If bit 0 of the following read command is ‘0’, the operation is single-track and
continues though index on the same track as defined for the applicable read
command.
If bit 0 of the following read command is ‘1’, the multitrack operation applies and
the operation depends on whether CKD conversion mode is specified.
If CKD conversion is specified, the multitrack operation is not allowed to
continue beyond the end of the last track in the cylinder.
– If the next track is not in the defined extent, execution is terminated with
unit check status. The sense data includes File Protected.
– If the next track is in the defined extent, execution is terminated with unit
check status. The sense data includes End-of-Cylinder.
If CKD conversion is not specified, the operation continues as described in
“Operations in the Domain of a Locate Record or Locate Record Extended” on
page 4-2.
Write Track – ‘0B’ Operation Code:
This operation code prepares the control
unit to update write the data area of record zero and format the remainder of the
track. The number of records to format is one less than the value specified in the
count parameter. After the last record is written on the track, the remainder of the
track is erased. If the value in the count parameter is ‘1’, only the data portion of
record zero is written, and the remainder of the track is erased.
If the file mask does not permit format write operations (bits 0 and 1 are ‘01’ or
‘10’), the command is rejected with unit check status. The sense data contains
command reject with format 0, message 2.
When track access completes, the control unit is oriented to home address. Prior
format write operations may cause the track to contain or not contain a Record
Zero (R0). In either case, Internal Disk next checks the search argument to assure
that it contains the expected value of the record ID field in the Record Zero count
area. The expected values of the search argument are:
CCHH value equal to the track that is to be written.
R value set to x'00'.
Unit check status with the sense data including No Record Found occurs if the
search argument is not as expected.
Chapter 4. Command Descriptions
4-23
Summary of Contents for Multiprise 3000
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