
Read Key and Data
Description:
The Read Key and Data command transfers the key and data areas
of a record to the channel.
If the control unit is oriented to a count area when the command starts, it sends the
key and data areas of the same record. If the control unit is not oriented to a count
area, it is oriented to the next count area (other than record zero) and sends the
key and data areas 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:
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 Read (16) or Read Data (06) 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 key and data areas 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 key and data areas 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 key and data areas of that
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 and
searches until either a user data record is found, or the operation is terminated
with an end-of-cylinder exception.
If the key length field in the count area contains zero, no key area transfer occurs.
Hex Code
Data Address
Count
0E
Multitrack
8E
The main storage location for the
first byte of the key data.
The number of key and
data bytes to be read.
4-66
Internal Disk Subsystem Reference Guide
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