Fujitsu M2488 Space command 11h, Space CDB Description, Space Field Description, Code Field Bits

M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS

4-3.29 SPACE command 11h

The Space command changes the logical unit position relative to the current position. The Code and Count fields determine how this relative positioning is to be performed. Before the position change occurs, any buffered write data and filemarks are written to the tape.

4-3.29.1 SPACE CDB Description

SPACE is a six-byte command. The bytes are shown below and described in Table 4-125. 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		1		0	0	0		1
1			LUN				Reserved			Code Field
2		MSB
3							Count Field
4													LSB
5					Reserved						Flag		Link

Note: Changeable fields in the CDB are shaded.

			Table 4-125. SPACE Field Description
BYTE	BIT	VALUE	DESCRIPTION
0	0-7	11h	Operation code.
1	0-2		The Code Field bits are described in Table 4-126.
2-4			The 3 byte Count Field is a 24-bit signed number (two’s complement). When the
			count field is 0, no position change occurs and buffered write data will not neces-
			sarily be written to tape. To force buffered write data to tape, issue a WRITE
			FILEMARK command with a count of 0.

		Table 4-126. Code Field Bits
CODE FIELD	TYPE		DESCRIPTION
000b	Space N Blocks		If the Count field is positive then space forward N blocks; N = Count. If the
			Count field is negative then space backward N blocks; N = -Count.
001b	Space N Filemarks		If the Count field is positive then position forward to the End-of-Tape side of
			the Nth filemark encountered; N = Count. If the Count field is negative then
			position backward to the Beginning-of-Tape side of the Nth filemark
			encountered; N = -Count.
010b	Space to N Sequential		If the Count field is positive then position forward to the End-of-Tape side of
	Filemarks		the next occurrence of N consecutive filemarks; N = Count. If the Count
			field is negative then position backward to the Beginning-of-Tape side of the
			next occurrence of N consecutive filemarks; N = -Count.
011b	Space to End-of-Data		The count field is ignored. Upon successful completion, the tape is posi-
			tioned such that a subsequent write command will append data after the last
			recorded block. If the tape is in 18-track format, end-of-data is defined as
			two sequential filemarks.

April 1997 CG00000-011503 REV. A 4-135