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3.2
Data Access Commands
3.2.1
READ (08)
Bit
7
Byte
0
1
2
3
4
5
0
This command reads the number of blocks of data in continuous logical data blocks specified
in the "Transfer block count" field with the logical data block on the disk media specified in
the "Logical block address" field in the CDB as the top.
The transfer block count can be specified up to a maximum of 256 logical data blocks. When
zero is specified in the "Transfer block count" field in byte 4 of the CDB, it specifies transfer
of 256 logical data blocks and when a value other than zero is specified, it specifies the
number of logical data blocks that should be transferred.
When transfer of multiple data blocks is instructed by this command, when the data blocks
which are to be processed come to a track boundary, cylinder boundary or zone boundary, a
head switch or cylinder switch is executed automatically and reading of the specified number
of blocks is performed.
When the specifications in the "Logical block address" field and "Transfer block count" field
in the CDB exceed the maximum logical block address in the IDD, that command is
terminated with a CHECK CONDITION status (ILLEGAL REQUEST [=5] / Logical block
address out of range [=21-00]) and the reading of data from the disk media is not executed.
Error recovery processing during execution of this command can be specified by the MODE
SELECT parameter. If retry processing and data correction processing are not prohibited,
when this command is completed normally, or when it is completed with a "RECOVERED
ERROR [=1]" sense key report, the data transferred to the INIT by this command are error
free. When a correctable error check is detected, the IDD first corrects the data errors in the
data buffer, then transfers those data to the INIT.
When disconnect processing is permitted, the starting timing for reconnection processing in
order to execute data transfer on the SCSI bus can be specified by the MODE SELECT
parameter (buffer full ratio). Also, if the Look-Ahead cache feature is permitted, a caching
operation is performed using the IDD's data buffer by this command. See Chapter 2, "Data
Buffer Management," concerning details of data buffer operation and the Look-Ahead cache
feature.
3 - 80
6
5
4
LUN
Logical Block Address
Logical Block Address (LSB)
Transfer Block Count
0
0
0
C141-E039-01EN
3
2
X'08'
Logical Block Address (MSB)
0
0
1
0
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