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8.17.1 Combined Header And Data (Mode 0000b)
In this mode a four byte header followed by data bytes are returned to the initiator during the DATA IN
phase. The Buffer ID and the buffer offset field are reserved.
The drive terminates the DATA IN phase when allocation length bytes of header plus data have been
transferred or when the header and all available data have been transferred to the initiator, whichever is
less.
The four-byte READ BUFFER header (see figure below) is followed by data bytes from the data buffer of
the drive.
Byte
7
6
0
1
(MSB)
2
3
Figure 124. READ BUFFER Header
The buffer capacity specifies the total number of data bytes that are available in the data buffer of the
drive. This number is not reduced to reflect the allocation length nor is it reduced to reflect the actual
number of bytes written using the WRITE BUFFER command.
Following the READ BUFFER header the drive will transfer data from its data buffer.
8.17.2 Read Data (Mode 0010b)
In this mode, the DATA IN phase contains buffer data.
! Buffer ID field must be set to zero, indicating the data transfer buffer. If another value is specified, the
command is terminated with CHECK CONDITION status. The drive shall set sense key to ILLEGAL
REQUEST and additional sense code to ILLEGAL FIELD IN CDB.
! Buffer Offset specifies the offset of the memory space specified by the Buffer ID. The initiator should
conform to the offset boundary requirements returned in the READ BUFFER descriptor. If the value
exceeds the buffer specified, the command is terminated with CHECK CONDITION status. The drive
shall set sense key to ILLEGAL REQUEST and additional sense code to ILLEGAL FIELD IN CDB.
! Allocation Length The drive terminates the DATA IN phase when allocation length bytes of data
have been transferred or when the header and all available data have been transferred to the initiator,
whichever is less.
8.17.3 Descriptor (Mode 0011b)
In this mode, a maximum of four bytes of READ BUFFER descriptor information are returned. The drive
returns the descriptor information for the buffer specified by the Buffer ID.
! Buffer ID field should normally be set to zero indicating the drive data transfer buffer. If any other
value is specified, the drive returns all zeros in the READ BUFFER descriptor.
! Buffer Offset field is reserved.
Bit
5
4
3
RSVD =
0
Buffer Capacity
Ultrastar 146Z10 hard disk drive specifications
130
2
1
0
(LSB)
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