
If the number of records written is equal to the number of data records on the
track, the count area read by a suffixed Read Count command is that of the
first record that was updated.
If the number of records written is not equal to the number of data records on
the track, the count area read by a suffixed Read Count command will be that
of the record that follows the last record updated. The ID of the first record
written is determined by referencing the record ID read, the number of records
updated, and the known sequence of the record IDs on the track.
Read Trackset – ‘0E’ Extended Operation Code:
This operation code prepares
the control unit to transfer all records from one or more tracks to the channel. The
tracks are specified by the extended parameter and the number of tracks is
specified by the Count Parameter.
The extended parameter length (bytes 18–19) must contain either X
'
0001
'
or
X
'
0002
'
, otherwise this command is rejected with unit check status. The sense
data contains command reject with format 0, message 4.
The extended parameter field must be one byte long (byte 20) if bytes 18–19
specified X
'
0001
'
, or two bytes long (bytes 20 and 21) if bytes 18–19 specified
X
'
0002
'
.
The extended parameter bytes contain a bit map which represents a set of
sequentially addressed tracks within the defined extent. Each bit represents one
track. A ‘1’ bit shows that all data on the specified track is to be read, a ‘0’ shows
that the specified track is to be skipped.
The first bit in the bit map must be ‘1’ and represents the track whose address is
specified in the seek address parameter (bytes 4–7). Subsequent addressed tracks
are in ascending order. The number of ‘1’ bits in the bit map must equal the value
in the Count Parameter (byte 3). If the first bit in the map is not a ‘1’, or the
number of ‘1’ bits do not equal the value in the count parameter, this command is
rejected with unit check status. The sense data contains command reject with
format 0, message 4.
All tracks in the bit map represented by a ‘1’ bit must be within the defined extents,
otherwise this command is rejected with unit check status. The sense data
includes File Protected.
Track access is initiated using the seek address and sector number parameters.
When completed, the search operation specified by the search argument and the
orientation modifiers (byte 0, bits 0–1) is performed.
Locate Record Extended must be followed by the number of Read Track
commands specified in the Count Parameter. If any other command sequence is
detected in the Locate Record Extended domain, the nonconforming command is
rejected with unit check status. The sense data contains command reject with
format 0, message 2.
The first Read Track command orients to the beginning of the first count area
(including R0) following the orientation established by the Locate Record Extended
command. Then it transfers each count, key and data area until it reaches
end-of-track.
Chapter 4. Command Descriptions
4-37
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