Read Data - IBM Multiprise 3000 Reference Manual

Read Data

Description: The Read Data command transfers the data area of a record to the
channel.
If the control unit is oriented to a count or key area when the command starts, it
sends the data area of the same record. If the control unit is not oriented to a
count or key area, it is oriented to the next count area (other than record zero) and
sends the data area of that record.
Chaining and Restrictions: Unit check status with the sense data containing
command reject with format 0, message 2 occurs if this command is:
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 state of
the multitrack bit (bit 0) in the CCW:
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 data length field in the count area contains zero, the control unit does not
send any data area. The command is terminated with channel end, device end,
and unit exception status.
4-68
Internal Disk Subsystem Reference Guide
Hex Code Data Address
06 The main storage location for the
Multitrack first byte of data.
86
Not preceded in the command chain by a Seek, Seek Cylinder, Locate Record,
Locate Record Extended, or a Read IPL command.
In a Locate Record or Locate Record Extended domain that specifies other
than a Read (16) or Read Data (06) operation or a Locate Record Extended
domain with a Read Any (0A) operation.
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 data 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 data 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 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 data area of that record. 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.)
Count
The number of data
bytes to be read.