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SDLT 600 SCSI Interface Guide Chapter 4: SCSI Commands

81-81200-02 REV A01 January 2005 4-83

Table 4-50. Data Compression MODE SELECT Page — Field Descriptions

Field Name Description

PS Parameters Savable. For MODE SELECT, must be set to 0.

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 Data Compression Page that follow this

field. The only valid value for this field is 0Eh.

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.

Specifying a value other than 10h for this field causes the drive to return

CHECK CONDITION status, Sense Key set to ILLEGAL REQUEST.

However, if the EEPROM parameter EnaRepDecomp is set, the drive

ignores the parameter in this field and does not return the CHECK

CONDITION status.

Decompression

Algorithm

Indicates which decompression algorithm the drive uses when

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

Specifying a value other than 10h for this field causes the drive to return

CHECK CONDITION status, Sense Key set to ILLEGAL REQUEST.

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