User Manual

SCSI Commands Reference Manual, Rev. J 134
www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)
3.15 READ (6) command
This command has been declared obsolete by the T10 committee. However, it is included because it may be implemented on
some products.
The READ (6) command (see table 95) requests that the device server read the specified logical block(s) and transfer them to the
data-in buffer. Each logical block read includes user data and, if the medium is formatted with protection information enabled,
protection information. Each logical block transferred includes user data but does not include protection information. The most
recent data value written, or to be written if cached, in the addressed logical blocks shall be returned.
The cache control bits are not provided for this command. Direct-access block devices with cache may have values for the cache control bits
that affect the READ (6) command; however, no default values are defined by this manual. If explicit control is required, the READ (10) com-
mand should be used.
LOGICAL BLOCK ADDRESS field
The LOGICAL BLOCK ADDRESS field specifies the first logical block accessed by this command. If the logical block address exceeds the capacity
of the medium the device server shall terminate the command with CHECK CONDITION status with the sense key set to ILLEGAL REQUEST and
the additional sense code set to LOGICAL BLOCK ADDRESS OUT OF RANGE.
TRANSFER LENGTH field
The TRANSFER LENGTH field specifies the number of contiguous logical blocks of data that shall be read and transferred to the data-in buffer,
starting with the logical block specified by the LOGICAL BLOCK ADDRESS field. A TRANSFER LENGTH field set to zero specifies that 256 logical
blocks shall be read. Any other value specifies the number of logical blocks that shall be read. If the logical block address plus the transfer
length exceeds the capacity of the medium, the device server shall terminate the command with CHECK CONDITION status with the sense key
set to ILLEGAL REQUEST and the additional sense code set to LOGICAL BLOCK ADDRESS OUT OF RANGE. The TRANSFER LENGTH field is con
-
strained by the MAXIMUM TRANSFER LENGTH field in the Block Limits VPD page.
a) For the READ (10) command, READ (12) command, READ (16) command, and READ (32) command, a TRANSFER LENGTH field set to zero
specifies that no logical blocks are read.
b) Although the READ (6) command is limited to addressing logical blocks up to a capacity of 2 Gigabytes, for block lengths of 512 bytes,
this command has been maintained since some system initialization routines require that the READ (6) command be used. System ini-
tialization routines should migrate from the READ (6) command to the READ (10) command, which is capable of addressing 2 Terabytes
with block lengths of 512 bytes, or the READ (16) command to address more than 2 Terabytes.
Table 95 READ (6) command
Bit
Byte
7 6 5 4 3 2 1 0
0
OPERATION CODE (08h)
1
Reserved (MSB)
2
LOGICAL BLOCK ADDRESS
3
(LSB)
4
TRANSFER LENGTH
5
CONTROL