Fujitsu M2488 manual Read Reverse command 0Fh, 18.1READ Reverse CDB Description

TAPE UNIT SCSI COMMANDS M2488 PRODUCT GUIDE

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.

** NOTE **

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.

4-3.18.1READ 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.

BITS

BYTES	7		6	5		4		3	2	1		0
0	0		0	0		0		1	1	1		1
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 4-74. READ REVERSE Field Description

BYTE	BIT	VALUE	DESCRIPTION
0	0-7	0Fh	Operation code.
1	0	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	1	1 or 0	Suppress Incorrect Length Indication (SILI) flag.
2-4			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.

4-80 CG00000-011503 REV. A April 1997