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Chapter 4 SCSI Commands

MODE SELECT (6) / (10) Command (15h / 55h)

DLT-S4 Interface Reference Guide 117

Table 71 Data Compression

MODE SELECT Page — Field

Descriptions

Field Description

PS Parameters Savable. For

MODE SELECT, must be set to 0.

SPF SubPage Format. Always set to 0. Indicates that this page uses the page_0 page

format.

Page Code Identifies the type of

MODE SELECT page being transferred. A value of 0Fh

identifies this as the Data Compression Page.

Page Length Indicates the number of bytes in the page, excluding 0 and 1. The length is returned

MODE SENSE commands and must subsequently be set to the same value when

performing

MODE SELECT.

DCE Data Compression Enable. Specifies whether the drive enables or disables data

compression. When set to 1, the drive compresses all data before writing it to tape.

When set to 0, the drive does not compress data before writing it to tape.

DCC Data Compression Capable. The

MODE SENSE command uses this bit to indicate

that the drive supports data compression.

DDE Data Decompression Enable. Must be set to 1. When the drive reads compressed

data from tape, it automatically decompresses the data before sending it to the host.

Data decompression must always be enabled.

RED Report Exception on Decompression. The drive does not report exceptions on

decompression (boundaries between compressed and uncompressed data). Must be

set to 00h.

Compression

Algorithm

Indicates which compression algorithm the drive uses to process data from the host

when the DCE bit (byte 02, bit 7) is set to 1. The only value currently supported for

this field is 10h.

Decompression

Algorithm

Indicates which decompression algorithm the drive uses when decompressing data

on the tape. The only value currently supported is 10h.

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