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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
in
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.