Product manual

3.6.9 Read Data Buffer command (3C
H
)
The Read Data Buffer command supports several different features. The
Read Data Buffer command can be used along with the Write Data Buffer
command to diagnose problems in the drive’s data buffer memory and
to test the integrity of the SCSI bus.
Note.
This command treats the buffer as a single segment, regardless of
the number of segments specified in mode page (08
H
). (Mode page
(08
H
), the Caching page, is described in Section C.6. on page 108).
Bytes
Bits
7654321 0
00011110 0
1 LUN 0 0 Mode
2 Buffer ID (00
H
)
3–5 Buffer offset
6–8 Allocation length
90000000 0
Byte 1
If the mode bits contain 000
B,
the initiator reads data from
the drive buffer. The data is preceded by a 4-byte header.
This mode is called
read combined header and data.
If the mode bits contain 010
B,
the initiator reads data from the
drive buffer without a header. This mode is called
read data.
If the mode bits contain 011
B,
a maximum of 4 bytes of
READ BUFFER descriptor information is returned. The
drive returns the descriptor information for the buffer speci-
fied by the buffer ID.
If there is no buffer associated with the specified buffer ID,
the drive returns all zeros in the READ BUFFER descriptor.
The buffer offset is reserved in this mode. The allocation
length should be set to four or greater. The drive transfers
the lesser of the allocation length or 4 bytes of READ
BUFFER descriptor.
READ BUFFER Descriptor
Bytes
Bits
7654321 0
0 Offset Boundary
1–3 (MSB) Buffer Capacity (LSB)
72 Medalist Pro 2160N/2160WC Product Manual, Rev. A