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M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS
April 1997 CG00000-011503 REV. A 4-135
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
Count Field
3
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
Filemarks
If the Count field is positive then position forward to the End-of-Tape side of
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.