M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS
April 1997 CG00000-011503 REV. A 4-63
4-3.14 READ command 08h
The READ command transfers one or more blocks to the initiator beginning with the next block on
the logical unit.
Upon termination of the READ command, the logical position is located after the last block trans-
ferred (EOM side).
4-3.14.1 READ CDB Description
READ is a six-byte command. The bytes are as shown below and described in Table 4-60. Com-
mon fields are described in paragraph 4-3.1 on page 4-4.
BITS
BYTES 7 6 5 4 3 2 1 0
0
0 0 0 0 1 0 0 0
1
LUN Reserved SILI Fixed
2
MSB
3
Transfer Length
4
LSB
5
Reserved Flag Link
Note: Changeable fields in the CDB are shaded.
Table 4-60. READ Field Description
BYTE BIT VALUE DESCRIPTION
0 0-7 08h Operation code.
1 0
0
1
The Fixed bit specifies both the meaning of the transfer length field and whether
fixed-length or variable-length blocks are to be transferred.
If the Fixed bit is zero, a single block is transferred with the bytes transferred
being the lesser of the actual block length or the requested transfer length.
If the Fixed bit is one, the transfer length specifies the number of blocks to be
transferred to the initiator.
1 1 Suppress Incorrect Length Indication (SILI) flag.
2-4
0
The Transfer Length indicates the number of bytes or blocks to transfer. The
block length used is the current block length specified in the mode parameters
block descriptor (refer to the Mode Select Block Descriptor in Table 4-47 on
page 7-53.)
When the transfer length is zero, no data is transferred and the current position
on the logical unit is not changed. This condition is not considered an error.
