User's Guide

Page 92 DDS-4 SCSI Interface Manual, Rev. B
Field
Name Bytes Bits Description
Block
Descriptor
Length
3 This field indicates the number of bytes of block descriptor information
that follow the parameter header.
If the DBD bit is set to 1, the block descriptor length is set to 0 (00h),
which indicates that no block descriptor is returned in the MODE
SENSE data.
If the DBD bit is set to 0, the block descriptor length is set to 8 (08h),
indicating that an eight-byte block descriptor is returned.
Medium Type Reporting
Byte 1 of the MODE SENSE header format as previously shown is the Medium Type
byte (accurate after tape motion completes after the initial tape insertion). This field
is available for reporting the cartridge type via the SCSI bus. Because tape format
selection is automatic, software applications do not usually need to know the tape
format. However, applications that need information about tape format and cartridge
type can use the Medium Type field and the Density Code field.
The values for the Medium Type byte are as follows:
33h DDS3 cartridge, MRS
34h DDS4 cartridge, MRS
35h DAT 72 cartridge, MRS
3Fh Non-DDS cartridge (cleaning cartridge)
The Medium Type field is currently defined as RESERVED in the ANSI SCSI-2
standard. This field has been used by QIC tape devices; the above values avoid
conflict with QIC drives.
Parameter List—Block Descriptor
The following table presents the block descriptor.
Byte
Bits
7 6 5 4 3 2 1 0
0 Density Code
1 0 0 0 0 0 0 0 0
2 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0
5 MSB—Block Length
6 Block Length
7 Block Length—LSB
Parameter List Block Descriptor Field Descriptions
The following table defines the fields in the block descriptor.
Field
Name Bytes Description