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SDLT 600 SCSI Interface Guide Chapter 4: SCSI Commands

81-81200-02 REV A01 January 2005 4-189

4.18 READ POSITION Command (34h)

The READ POSITION command reads a position identifier or SCSI Logical Block Address (LBA).

The LOCATE command uses this identifier or LBA for high-performance repositioning of the tape

medium to a known logical position.

Figure 4-99. READ POSITION Command Descriptor Block — Data Format

Bit

Byte

7 6 5 4 3 2 1 0

0 Operation Code (34h)

1 Reserved Service Action

2 – 6 Reserved

7 – 8

(MSB)

Allocation Length

(LSB)

9 Control

Table 4-110. READ POSITION Command Descriptor Block — Field Descriptions

Field

Name Description

Service

Action

Determines the format of the positional data the drive returns. All values other than those listed

below are reserved.

Value Description

00h The drive returns 20 bytes of data in the format described in “Read Position Data —

Short Form” on page 4-190.

01h The drive returns 20 bytes of data in the format described in “Read Position Data —

Short Form” on page 4-190.

06h The drive returns 32 bytes of data in the format described in “Read Position Data —

Long Form” on page 4-192.

Allocation

Length

Valid only when Service Action is set to 08h. The value in this field specifies the maximum

length of the parameter data the drive returns. If the value in this field is not sufficient to

contain all of the returned parameter data, the drive returns truncated parameter data.

SDLT 600

SCSI Interface Guide

SCSI Commands

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REV A01

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Quantum 1200 Series DAT Autochanger Guide de l'utilisateur Page 231