User's Guide

Page 74 DDS-4 SCSI Interface Manual, Rev. B
Command Descriptor Block Field Description
The following table defines the fields in the CDB.
Field Name
Bytes Bits Description
PF bit 1 4 The Page Format (PF) bit indicates whether the drive should
interpret the MODE SELECT parameters that follow the CDB and
the header as SCSI-1 or as SCSI-2 parameters. For the Scorpion
40 drives, the PF bit must be set to 1 (SCSI-2).
Parameter List
Length
4 This field specifies the number of bytes in the MODE SELECT
parameter list that are transferred from the host to the drive
during a Data-Out Phase. A Parameter List Length of zero
specifies that no data is to be transferred. This length is valid and
is not considered an error. A length in this field that truncates a
parameter list (as returned in a MODE SENSE command) causes
the drive to return a Check Condition, and the request sense data
is set to Illegal Request.
MODE SELECT Parameters
The parameter list for the MODE SELECT command contains
• A four-byte header, followed by
• Zero or one eight-byte Block Descriptor, followed by
• Zero or more variable-length pages.
The following table illustrates the structure of the mode select parameter list.
Byte
Bits
7 6 5 4 3 2 1 0
0
.
.
3
Parameter List Header
4
.
.
11
Block Descriptor
12
.
.
.
n
Mode Pages
The following table shows the Parameter List Header format.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0
2 0 BUFFERED MODE 0 0 0 0
3 Block Descriptor Length