Pioneer SCSI-2 - Manual (Page 98)

Read Buffer
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2.20 Read Buffer (3Ch)
Operation Code is (3Ch).
Mode specifies meaning of the Buffer Offset field.
Buffer ID is not supported. This byte is always 00h.
Buffer Offset
The byte offset in the buffer at which the read shall begin. This must be between 0 and 15.
Allocation Length must include 4 byte header.
This command is used with the WRITE BUFFER command to test the reliability of the drive
command buffer memory and of the SCSI bus. This command does not cause a disc access. The
drive terminates the DATA IN phase when it has transferred the header and data specified in
Allocation Length, or the header and the remainder of the buffer.
Mode field Definition
00b The header, data, and buffer offset are 0s.
01b The buffer offset indicates the offset from the start of the
buffer at which the data are to be read.
10b Reserved
11b Reserved
The 4-byte header and the following data are transferred to the initiator in the DATA IN phase.
If Allocation Length is 0, neither the header nor data are transferred.
The header is defined as follows:
- Effective Length
The number of bytes of valid data in the buffer.
The effective length does not depend on the actual number of data written by a WRITE BUFFER
command. The sum of the buffer offset plus the effective data length is always 16. The number
of data to be transferred following the header is the smaller one, either the allocated length minus
4 bytes, or the effective length.
When the drive cannot accept the specified buffer offset, a Check Condition is returned with the
sense key "ILLEGAL REQUEST." If Buffer Offset is not 0 when Mode is set to 00h, Check
Condition is returned.