User's Guide

Page 150 DDS-4 SCSI Interface Manual, Rev. B
SEEK BLOCK (0Ch)
The SEEK BLOCK command is used to position the tape to the specified block
address in the current partition. No data is transferred. SEEK BLOCK positions the
tape to block locations greater or less than the current block position. Positioning is
done with a high speed search and does not require a sequential read for the
requested block.
The Initiator may obtain block addresses through the REQUEST BLOCK ADDRESS
command as part of its tape write procedures. The block addresses can, in turn, be
recorded in a user-defined directory.
When there is no exception condition during a SEEK BLOCK command, the tape is
logically positioned before the block specified in the block address. The first logical
block on tape is block 1; therefore, a zero in the block address is considered an
error.
SEEK BLOCK Command Descriptor Block
The following table shows the layout of the CDB.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 0 1 1 0 0
1 0 0 0 0 0 0 0 IMMED
2 MSB—Block Address
3 Block Address
4 Block Address—LSB
5 vendor unique* 0 0 0 0 Flag Link
* This vendor-unique field is reserved and must be set to zero.
Command Descriptor Block Field Description
The following table provides descriptions of the CDB fields.
Field
Name Bytes Bits Description
IMMED 1 0 If this bit is 1, the status is returned as soon as the operation is initiated.
If this bit is 0, the status is returned after the tape is positioned at the
specified block.
Block
Address
2-4 These fields specify the address of the block to which the tape is to be
positioned.