User's Guide

Page 90 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
DBD bit 1 3 If the Disable Block Descriptors (DBD) bit is set to 0, the drive always
returns the block descriptor in the MODE SENSE data.
If the DBD bit is set to 1, the drive does not return the block descriptor
in the MODE SENSE data.
NOTE: When the DBD is 1, the Block Descriptor Length in the
parameter header is set to 0.
PC field 2 6-7 The Page Control field defines the type of parameter values to be
returned. Valid values are:
76 Unit
00 Report current values
01 Report changeable values
10 Report default values
11 Report saved values
Note: the default values are always the saved values.
If parameter type 00 (report current values) is specified, the drive
returns its current configuration to the host.
If parameter type 01 (report changeable values) is specified, any
values that may be altered by a subsequent MODE SELECT
command are returned. Any bit that can be changed is set to 1;
otherwise, the bits are set to 0.
If parameter type 10 (report default values) is specified, the drive
returns its default (power-up or reset) configuration.
Page Code 2 0-5 The Page Code field lets the initiator select the page or pages to be
returned by the drive. If Page Code is 0, only the 4-byte header and 8-
byte block descriptor are returned.
Hex Page Name
00 No page returned
02 Disconnect/Reconnect
0A Control Mode
0F Data Compression Control
10 Device Configuration
11 Medium Partition
1C Tape Alert
1D Element address assignment (Autoloader only)
1F Device Capabilities (Autoloader only)
3F All available pages
Allocation
Length
4 The Allocation Length field specifies the number of bytes the host has
allocated for returned MODE SENSE data. An Allocation Length of 0
(00h) means that no parameter list data bytes are returned to the
host. This condition is not considered an error.
The drive terminates the Data In phase in one of two ways based on
whichever is less:
• When Allocation Length bytes have been transferred.
• When all available data have been transferred to the initiator.