
Read Count
Description:
The Read Count command transfers the count area of a record,
other than record zero, to the channel.
The control unit is oriented to the next count area and sends that count area to the
channel.
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 a Locate Record or Locate Record Extended domain that specifies other
than a Write Data (01), Read (16), or Read Data (06) operation or in a Locate
Record Extended domain that specifies other than a Read Any (0A) or Write
Any (09) operation.
If end-of-track is detected before a count area is found when in a Locate Record or
Locate Record Extended domain, the operation continues according to the
multitrack bit (bit 0) in the CCW:
If the multitrack bit is ‘0’, the control unit is oriented to the count field of the first
user data record on the same track. It sends the count area of the record to
the channel. If the track does not have a user data record, 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. It sends
the count area of the first user data record to the channel. (See “Operations in
the Domain of a Locate Record or Locate Record Extended” on page 4-2.) If
the track does not have a user data record, the command is terminated with
unit check status. The sense data includes No Record Found.
If end-of-track is detected before a count area is found when not in a Locate
Record or Locate Record Extended domain, the operation continues according to
the multitrack bit (bit 0) in the CCW:
If the multitrack bit is ‘0’, the control unit is oriented to the count area of the first
user data record on the same track. It sends the count area to the channel. If
the track does not have a user data record, 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
searches until either a user data record is found, or 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.)
Ending Status:
The control unit presents channel end and device end status
when data transfer completes. When the command completes, the control unit is
oriented to the count area that transferred.
Hex Code
Data Address
Count
12
Multitrack
92
The main storage location for the
first byte of the count area.
8
4-70
Internal Disk Subsystem Reference Guide
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