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Chapter 8 SCSI Commands
8.11. READ BUFFER Command (3Ch)
In combination with the WRITE BUFFER command, the READ BUFFER
command is used to perform diagnostics such as testing the autoloader memory
and SCSI INTEGRITY.
Table 8.11.1 : READ BUFFER command
The function of this command and the meaning of the fields in the Command
Descriptor Block depend on the value of the Mode field. Table 8.11.2 shows the
Mode field values supported by the autoloader.
Table 8.11.2 : READ BUFFER mode field
8.11.1. Combined header and data mode (0000b)
During the DATA IN phase of the Combined Header and Data Mode, a 4-byte
header followed by data is transferred to the host. The Buffer ID and Buffer
offset field are reserved.
The 4-byte READ BUFFER header is shown in Table 8.11.1.1. After, the
autoloader transfers data from its data buffer.
Table 8.11.1.1 : READ BUFFER header
Bit
Byte
7
6
5
4
3
2
1
0
0
Operation code (3Ch)
1
Logical unit number(0h)
Reserved
Mode
2
Buffer ID(00h)
3
(MSB)
Buffer offset
4
5
(LSB)
6
(MSB)
Allocation length
7
8
(LSB)
9
Control(0h)
Mode
Description
0000b
Combined header and data
0010b
Data
1010b
Echo Buffer
1011b
Echo Buffer descriptor
Bit
Byte
7
6
5
4
3
2
1
0
0
Reserved
1
(MSB)
Buffer capacity
3
(LSB)
