READ BUFFER (3Ch)
The READ BUFFER command is used in conjunction with Write Buffer as a diagnostic function for testing
the media changer’s data buffer and the SCSI bus integrity. It is also used to read out Vendor Specific
settings.
Bit 7 6 5 4 3 2 1 0
Byte
0 Operation Code (3Ch)
1 LUN Reserved Mode
2 Buffer ID
3 (MSB)
4 Buffer offset
5 (LSB)
6 (MSB)
7 Allocation Length
8 (LSB)
9 Control
Field descriptions:
Mode: The Mode field is used to select the mode of operation. The media changer supports the following
values within the field.
0001b Vendor Unique operation
0010b Data
0011b Descriptor
1010b Echo buffer
1011b Echo Descriptor
If any non supported value is set, the media changer terminates the command with a Check
Condition status and an Illegal Request sense key set.
Buffer ID:
For all modes only buffer ID zero is supported.
Buffer Offset:
The Buffer Offset field is not supported and must be set to zero. If the Buffer Offset field specifies
an unsupported value, the media changer shall return Check Condition status. The sense key will
be set to ILLEGAL REQUEST and the sense data to INVALID FIELD IN CDB.
Allocation Length:
The Allocation Length specifies the maximum number of bytes that the initiator has allocated for
returned data.
Vendor Unique Mode
A READ BUFFER command with the mode set to Vendor Unique Mode is used to retrieve parameters
stored in non volatile Ram. The Buffer ID specifies the requested page. The Buffer Offset field in the CDB
is not supported for this mode.
Buffer ID Description Parameter List Length
00h Variables Setting page 002Eh
3-50 TL2000 and TL4000 SCSI Reference
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