Read Home Address
Description:
The Read Home Address command transfers a partial home
address area to the channel.
The control unit is oriented to index when the Read Home Address command
starts. A 5-byte home address transfers to the channel. These 5 bytes are the flag
byte and the 4-byte track address bytes (CCHH) as shown in Table 4-24.
When the multitrack bit (bit 0) in the CCW is ‘0’, the control unit is oriented to index
and sends the home address to the channel. If the multitrack bit is ‘1’, the control
unit is oriented to index, advances to the next track, and sends the home address
of that track to the channel. (See “Operations Outside the Domain of a Locate
Record or Locate Record Extended” on page 4-3.)
Note:
Since the Read Home Address command always causes the control unit to
be oriented to index before it transfers data, a multitrack Read HA
command always causes the control unit to switch to the next track before it
transfers any data.
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 Data (06), or a Read (16) operation and index orientation (byte 0,
bits 0 and 1 are ‘11’).
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 home address.
Hex Code
Data Address
Count
1A
Multitrack
9A
The main storage location of the
home address.
5
Table
4-24. 5-Byte Section of Home Address Definition
Bytes
Definition
0
Flag, not used, set to zero.
1–4
Track address (CCHH)
4-62
Internal Disk Subsystem Reference Guide
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