
Search Argument – Bytes 8–12
Bytes 8 through 12 specify the cylinder, head, and record (CCHHR). These bytes
specify a value to be used as a search argument for the Locate Record Extended
search operation. See “Search Operation” on page 4-19.
When the operation (byte 0) does not need orientation to a specific record, no
search operation occurs and bytes 8 through 12 are ignored. When home address
orientation is specified, byte 12 is ignored.
Sector Number – Byte 13
Byte 13 contains a sector number. The control unit uses this sector number for
positioning in the track image. The sector number must be valid for the logical
volume. If the sector number is invalid, 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 range of valid sector
numbers.
If the sector number is zero, the next command starts with the device in a position
immediately before index. A value of X
'
FF
'
is valid and specifies that sector
positioning is not to be performed before establishing orientation.
Transfer Length Factor – Bytes 14–15
When byte 1, bit 0 is ‘1’, bytes 14 and 15 contain a transfer length factor. The
control unit uses the transfer length factor to determine the number of data bytes to
request from the channel for each write command that follows a Locate Record
Extended command specifying Write Data (01). The product of the value in bytes
14 and 15 and the count parameter determines the total number of bytes to be sent
in a Locate Record Extended domain specifying Format Write (03), Write Track
(0B), or Read (16).
The control unit does not keep the transfer length factor value after the end of the
Locate Record Extended domain. If a transfer length factor was not specified in the
Locate Record Extended command, the control unit uses the value from the Define
Extent blocksize parameter for the data transfer length.
Unit check status with the sense data containing command reject, with format 0
message 4 occurs if:
Byte 1, bit 0 is a ‘0’, and bytes 14 and 15 do not contain zeros.
Byte 1 bit 0 is a ‘1’, and bytes 14 and 15 do not contain a nonzero value.
The transfer length factor value is more than the value specified (or implied) in
the Define Extent blocksize parameter.
Not Used – Byte 16
Byte 16 must contain zeros. If byte 16 does not contain zeros, the Locate Record
Extended command is rejected with unit check status. The sense data contains
command reject with format 0, message 4.
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Internal Disk Subsystem Reference Guide
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