M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS
April 1997 CG00000-011503 REV. A 4-75
4-3.17 READ POSITION command 34h
The READ POSITION command causes 20 bytes to be sent from the target to the initiator. The 20
bytes are a report of the position of the tape unit and information about blocks stored in the buffer;
the format of this data is shown in paragraph 4-3.17.2 on page 4-76.
This command can be executed when no tape cartridge is loaded or when the tape unit is not ready.
No tape movement is initiated due to this command.
4-3.17.1 READ POSITIO N CDB Descri ption
READ POSITION is a ten- byte command. The bytes are shown below and described in Table 4-
70. Common fields are described in paragraph 4-3.1 on page 4-4.
BITS
BYTES 7 6 5 4 3 2 1 0
00 0 1 1 0 1 0 0
1LUN Reserved BT
2Reserved
3Reserved
4Reserved
5Reserved
6Reserved
7Reserved
8Reserved
9Reserved Flag Link
Note: Changeable fields in the CDB are shaded.
Table 4-70. READ POSITION Field Description
BYTE BIT VALUE DESCRIPTION
0 0-7 34h Operation code.
1 0 The BT bit dictates the format of values reported in the First Block Loca-
tion and Last Block Location fields of the return data.
0 Values in First Block Location and Last Block Location are to be reported
as Logical block addresses. The first filemark or data block on tape is
assigned logical block address 0; logical block addresses increase by 1 for
each data block and filemark thereafter. The maximum Logical block
address is 3FFFEFh.
1 Values in First Block Location and Last Block Location are to be reported
as Device specific block addresses (also known as Block IDs). The format
of these device specific block addresses are shown in paragraph4-3.17.3
on page 4-78.