Quantum DLT1/VS80 SCSI, Interface Manual

Page: 132 / 182

Chapter 4: SCSI Commands
4-90 July 2004 81-81276-01 Rev A01
4.14.1 Combined Header and Data Mode
In this mode, the tape drive returns a 4-byte header followed by the data bytes. The tape drive
terminates the DATA IN phase when it has transferred Allocation Length bytes of header and data or
when it has transferred all available data to the initiator, whichever is less. Data bytes from the target
data buffer follow the 4-byte READ BUFFER header. The header has the following format:
Figure 4-61. READ BUFFER Header for Combined Header and Data Mode — Data Format
Table 4-54. READ BUFFER (3Ch) Command Descriptor Block — Field Descriptions
Field Name Description
LUN Logical Unit Number. The target ignores this field. Only an IDENTIFY message
can change the LUN.
Mode The tape drive supports the following values within the field. If any unsupported
value is set, the tape drive terminates the command with a CHECK CONDITION
status and an ILLEGAL REQUEST Sense Key set.
Mode Description
000b Combined Header and Data
010b Data
011b Descriptor
Buffer ID The tape drive supports only a single Buffer ID field of 0. If this field is nonzero,
the tape drive returns a CHECK CONDITION status with an ILLEGAL
REQUEST Sense Key set.
Offset The tape drive does not support offsetting of data. If this field is nonzero, the tape
drive returns a CHECK CONDITION status with an ILLEGAL REQUEST Sense
Key set.
Allocation Length This field specifies the maximum number of bytes that the initiator has allocated
for returned data.
Bit
Byte
7 6 5 4 3 2 1 0
0 Reserved
1 - 3
(MSB)
Available Length
(LSB)