4-3.18 Read Reverse Command 0Fh; 4-3.18.1 Read Reverse Cdb Description; Table 4-74. Read Reverse Field Description - Fujitsu M2488 Product Manual

TAPE UNIT SCSI COMMANDS
4-3.18 READ REVERSE command 0Fh
The READ REVERSE command requests that the tape unit transfer blocks of data to the initiator.
Any buffered write data or filemarks are written before this operation is executed. This command is
similar to the READ command except that the direction of the read is reversed; blocks are transferred
starting from the current position and progressing towards BOT.
It is recommended that this command not be used extensively. The
overall execution time of the READ REVERSE command is exces-
sive due to the extra tape positioning involved.
4-3.18.1 READ REVERSE CDB Description
READ REVERSE is a six-byte command. The bytes are shown below and described in Table 4-
74. Common fields are described in paragraph 4-3.1 on page 4-4.
BYTES 7
0
0
1
2 MSB
3
4
5
Note: Changeable fields in the CDB are shaded.
BYTE BIT VALUE
0 0-7
1 0
1 1
2-4
4-80
** NOTE **
6 5 4
0 0 0
LUN
Transfer Length
Reserved

Table 4-74. READ REVERSE Field Description

0Fh Operation code.
1 or 0 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 or 0 Suppress Incorrect Length Indication (SILI) flag.
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 parame-
ters block descriptor (refer to the Mode Select Block Descriptor in Table 4-
47 on page 4- 53.)
When the transfer length is zero, no data is transferred and the current posi-
tion on the logical unit is not changed. This condition is not considered an
error.
CG00000-011503 REV. A
M2488 PRODUCT GUIDE
BITS
3 2
1 1
Reserved
DESCRIPTION
1 0
1 1
SILI Fixed
LSB
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April 1997