Xdwrite Command (50H) - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
5.56

XDWrite command (50h)

The XDWrite command (see Table 180) requests that the target Xor the data transferred to it with the data on
the medium. The resulting Xor data is stored in the target's buffer. The disposition of the data transferred from
the initiator is controlled by the disable write bit.
The resulting Xor data is retained in the target's buffer until it is retrieved by an XDRead command with starting
logical block address and transfer length fields that match the starting logical block address and transfer length
of this command. For additional information about Xor commands, see Section 5.55.1.
Table 180: XDWrite command (50h)
Bit 7
Byte
0 Operation Code (50h)
1
2 (MSB)
3
4
5
6 Reserved
7 (MSB)
8
9 Control [6]
Notes.
[1] If the Disable Page Out (DPO) bit is set to one, no data is cached. The DPO bit is only meaningful if the
RCD bit of Mode Select Page 8 is set false (caching enabled).
[2] A Force Unit Access (FUA) bit of one indicates that the Write command shall not return Good status until
the logical blocks have actually been written on the media. The FUA bit is only meaningful if the WCE bit
of Mode Sense page 8 is true.
[3] A Disable Write bit of zero indicates that the data transferred from the initiator shall be written to the
medium after the Xor operation is complete. A Disable Write bit of one indicates that the data shall not be
written to the medium.
[4] The Logical Block Address specifies the logical block at which the write operation shall begin.
[5] The Transfer Length field specifies the number of logical blocks that shall be transferred to the XDWrite
target for the Xor operation. It also specifies the number of blocks to be written to the medium after the Xor
operation.
[6] See "Control byte," paragraph 4.2.6.
6 5
Reserved
4 3
DPO [1] FUA [2]
Logical Block Address [4]
Transfer Length [5]
2 1
Disable
Reserved
Write [3]
225
0
(LSB)
(LSB)