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SCSI Commands: 48BSPACE
Page
211
3.36
SPACE
The SPACE command uses three methods to move the tape. This command moves
the position:
Forward or backward a specified number of blocks.
Forward or backward a specified number of filemarks.
Forward to the end of recorded data (EOD).
If the target block or filemark is in the buffer of the drive, no tape motion results,
otherwise, spacing is done at high search speed.
3.36.1
SPACE Command Descriptor Block
Byte
Bits
7 6 5 4 3 2 1 0
0 Operation
Code
(11h)
1 Ignored
LUN
Reserved
Code
2 (MSB)
3
4
Count
(LSB)
5 Control
3.36.1.1
SPACE Command Field Descriptions
Field
Bytes
Bits
Description
Operation
Code
0
The Operation Code for SPACE is 11h.
Ignored
Logical
Unit
1
5-7
The LUN field is vestigial from the SCSI-1 standard and is ignored.
Code
1
0-2
000b = Move Count blocks
001b = Move Count filemarks
011 = Move to end of recorded data (EOD)
Count 2-4
This field specifies the number of blocks or filemarks to space over.
A positive Count moves the tape forward. A negative (2's
complement) Count moves the tape backward. A zero Count
causes no media movement and is not an error. For Space to EOD
operation, this field is ignored.
Reserved
All reserved bits must be 0.
Control 5
See
SCSI Command Control Byte Format on page 25.
The SPACE command instructs the drive to set a new logical position relative to the
current logical position. How this is done is dependent on the value of the Code field
and the Count field. The Count field is a signed value indicating the distance to
move, negative indicating movement towards BOM and positive indicating
movement towards EOM.
If the Code field is 000b, then the logical position is moved the number of blocks
indicated by the Count field. If a file mark is detected between the current logical
position and the requested logical position, the new logical position is set to
immediately after the file mark in the direction of the space operation. If BOM or
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