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Chapter 8 SCSI Commands
8.22. WRITE BUFFER Command (3Bh)
The WRITE BUFFER command is used in parallel with the READ BUFFER
command to performs an autoloader memory and SCSI Bus Integrity test.
Table 8.22.1 : WRITE BUFFER command
8.22.1. Mode
The function of this command and the meaning of the fields within the
COMMAND DESCRIPTOR BLOCK are determined by the Mode field. The
Mode field is defined as follows.
Table 8.22.1.1 : WRITE BUFFER mode field
8.22.2. Combined header and data mode (0000b)
A 4-byte header is transferred first in the Combined Header And Data Mode.
The 4-byte header consists only of reserved bytes. The Buffer ID and Buffer
Offset are 0. The Parameter List Length field is the number of bytes transferred
in the DATA OUT phase. Because this value includes the four bytes of the
header, the amount of data transferred to the autoloader buffer is obtained by
subtracting 4 from this value. Moreover, the host does not set the Parameter List
Length to a value exceeding the result of adding 4 to the buffer value returned
in the header of the READ BUFFER command with Mode0000b. For a
Parameter List Length exceeding the autoloader buffer capacity, the autoloader
terminates the command with a CHECK CONDITION status. The sense key is
ILLEGAL REQUEST. Data transferred in this mode may be overwritten by
another command or the like, and is not guaranteed data. To guarantee the data,
the autoloader must first be reserved, be issued a WriteBuffer command, and
then a ReadBuffer command.
Bit
Byte
7
6
5
4
3
2
1
0
0
Operation code (3Bh)
1
Logical unit number(0h)
Reserved
Mode
2
Buffer ID(0h)
3
(MSB)
Buffer offset
4
5
(LSB)
6
(MSB)
Parameter list length
7
8
(LSB)
9
Control(0h)
Mode
Description
0000b
Write combined header and data
0010b
Write data
1010b
Echo Buffer
