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CDU-541 CD-ROM DRIVE SCSI INTERFACE MANUAL
5 .
2 •
36.
WRITE BUFFER Command
==============================================================================
Bit
I
Byte
I
7
6
5
4
3
2
1
o
==============================================================================
o
I
I
Operation Code (3Bh)
-----1-----------------------------------------------------------------------
1
I
Logical Unit Number
:
Reserved
:
Mode
-----1-----------------------------------------------------------------------
2
:
Reserved
3
(MSB)
4
Buffer Offset
5
(LSB)
-----1-----------------------------------------------------------------------
6
I
(MSB)
-----+---
---I
7
I
Transfer Length
I
-----1---
---I
8
I
(LSB)
I
-----1-----------------------------------------------------------------------1
9
I
Control Byte
I
==============================================================================
The WRITE BUFFER command is used in conjunction with the READ BUFFER command
as a diagnostic function for testing controller memory and the bus integrity.
This command will not alter the medium.
The function of this command and the meaning of fields within the command
descriptor block depend on the contents of the mode field.
A mode field value
of zero indicates that the buffer offset is zero.
A mode field value of one
indicates that the buffer offset is valid and the data will be placed in the
buffer with that offset.
The buffer offset is the byte offset within the buffer where the data will
be stored.
If the controller is unable to accept the specified buffer offset,
it will return CHECK CONDITION status.
The sense key is set to ILLEGAL
REQUEST and the additional sense code is set to ILLEGAL VALUE IN CDB.
The data to be transferred is preceded by a four-byte header.
The header
consists of all reserved bytes.
The transfer length specifies the maximum
number of bytes that will be transferred during the DATA OUT phase.
This
number includes four bytes of WRITE BUFFER header, so the data length to be
stored in the controller's buffer is transfer length minus four.
If the
transfer length minus four exceeds the capacity of the buffer the controller
will return a CHECK CONDITION status.
The sense key is set to ILLEGAL REQUEST
and the additional sense code is set to ILLEGAL VALUE IN CDB.
5-63
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