Read Multiple Count, Key, and Data
Description:
The Read Multiple Count, Key, and Data command transfers the
next record (excluding R0) and all remaining records on the track to the channel.
The byte count value should be at least as large as the maximum size record that
can be written on the track. If a data length area is zero, the control unit neither
sends the data field nor presents exception status, and the read operation
continues with the next count area on the track.
This command is for use by dump/restore programs. The ability to start the data
transfer at other than the beginning of the track is for ERP restart.
The control unit is oriented to the start of the count area of the next user data
record. It sends each count, key, and data area on the track until end-of-track. If
end-of-track is detected before a count area is found, no data transfer occurs. The
control unit presents channel end and device end status, and does not report an
exception condition.
If the channel truncates data transfer (the CCW byte count went to zero), the
control unit continues reading data until the end of the current track, then presents
channel end and device end status. The control unit does not report an exception
condition when the channel truncates data transfer. If an exception condition
occurs after the channel truncates data transfer, the status includes channel end,
device end and unit check.
If a read or search command (other than Read Multiple CKD) follows a Read
Multiple CKD command, the control unit orients to index before beginning execution
of that next command. If another Read Multiple CKD command follows a Read
Multiple CKD command, the operation of the second Read Multiple CKD is not
predictable.
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.
Ending Status:
The control unit presents channel end and device end status
when data transfer completes.
Hex Code
Data Address
Count
5E
The main storage location for the
first byte of data.
At least as large as the maximum
size record.
Chapter 4. Command Descriptions
4-71
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