Write Home Address
Hex Code
Data Address
Count
19
The main storage location of the home address.
5
Description:
The Write Home Address command simulates updating the home
address record on the track, by verifying a 5-byte section of the home address
record. This 5-byte section consists of a flag byte and a 4-byte track address
(CCHH). Home Address is not written on the device. The 5-byte section of home
address area is shown in Table 4-25.
The control unit requests 5 bytes of home address data from the channel. If the
channel sends fewer than a 5-byte home address, the command is rejected with
unit check status. The sense data contains command reject with format 0,
message 3. The existing HA, R0, and user data records on the track are not
affected.
Each track has one home address area to establish track identity. If this command
is not followed by a Write R0 command, the remaining portion of the track is
erased.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is not in a Locate Record or Locate Record Extended domain,
and is not preceded by a Search Home Address Equal command that
compared equal on all 4 bytes of the track address field.
The file mask does not permit writing HA (bits 0 and 1 not ‘11’).
This command is in a Locate Record or Locate Record Extended domain
specifying other than a Format Write (03) operation and home address
orientation (byte 0, bits 0 and 1 are ‘01’).
The control unit verifies the home address data from the channel as follows:
Bits 0 through 7 of the flag byte must be zero.
The track address must equal the address of the currently accessed track.
If the home address data is not valid, the command is rejected with unit check
status. The sense data contains command reject with format 0, message 4. The
existing HA, R0, and user data records on the track are not affected.
Ending Status:
If additional commands are expected within the domain of a
Locate, device end will be presented with channel end. Otherwise channel end will
be presented when the Home Address data is validated. The control unit is
oriented to home address when the command completes.
Table
4-25. 5-Byte Section of Home Address Definition
Bytes
Definition
0
Flag, must be zero.
1–4
Track address (CCHH)
4-84
Internal Disk Subsystem Reference Guide
Summary of Contents for Multiprise 3000
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