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Chapter 8 SCSI Commands
8.12.6. Data transfer element descriptor
Table 8.12.6.1 specifies the contents of the Data Transfer Element Descriptor.
Table 8.12.6.1 : Data transfer element descriptor
An Access bit of 1 indicates that access to the element by the Medium Transport
Element is permitted. An Access bit of 0 indicates that access to the element by
the Medium Transport Element is inhibited.
Note
Access to the Data Transfer Element (Tape Drive) by the Medium Transport
Element is refused during data transfer. Also, this bit does not accurately reflect
the state of the Data Transfer Element (Tape Drive), but simply indicates
whether the autoloader can mechanically access the element.
A Not This Bus (not bus) bit of 1 indicates that the SCSI Bus Address and
Logical Unit Number of the SCSI bus selected by the autoloader are invalid. A
Not This Bus (not bus) bit of 0 indicates that the SCSI Address and Logical Unit
Number are from the same SCSI bus as the autoloader and are valid. Because
the SCSI bus and Data Transfer Element (Tape Drive) SCSI bus are inside the
autoloader, this is always 0.
An ID Valid bit of 1 indicates that the SCSI Bus Address value is valid. An LU
Valid bit of 1 indicates that the Logical Unit Number value is valid.
The SCSI Bus Address field is the SCSI Address of the Data Transfer Element
(Tape Drive) supported by the autoloader and specified by the Element Address.
The Logical Unit Number field is the Logical Unit Number in the Data Transfer
Element (Tape Drive) supported by the autoloader and specified by the Element
Bit
Byte
7
6
5
4
3
2
1
0
0
(MSB)
Element address
1
(LSB)
2
Reserved(0h)
Access Except
Reserved
Full
3
Reserved(0h)
4
Additional sense code
5
Additional sense code qualifier
6
Not bus
Reserved
ID valid LU valid
Reserved
Logical unit number
7
SCSI bus address
8
Reserved(0h)
9
SValid
Invert
Reserved(0h)
10
(MSB)
Source storage element address
11
(LSB)
12
Primary volume tag information
(Field omitted if PVolTag = 0)
47
48
Reserved
(field moved up if Primary Volume
Tag Information field is omitted)
51
52
Tape Drive Serial Number
(omitted if S/N bit=0)
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