Read Data Buffer Command (3C H ) - Seagate MEDALIST 1080SL Product Manual

62 Medalist 1080sl SCSI Product Manual, August 1995
3.5.9 Read Data Buffer command (3C
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
page (08 ), the Caching page, is described in Section C.5.3.]
H
Bytes
7 6
0 0 0
1 LUN
2
3–5
6–8
9 0 0
Byte 1 If the mode bits contain 000
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
drive buffer without a header. This mode is called read data .
All other settings for the mode bits are reserved.
Byte 2 The buffer ID is not supported and must always be zero.
Byte 3–5 The buffer offset is added to the starting address of the
buffer to determine the source of the first data byte. The
bytes that follow are read from sequential addresses. If the
sum of the buffer offset and the transfer length exceeds the
available length reported in the Read Buffer header (see
Section 3.5.9.1), the drive transfers all the data contained
in the buffer.
Bytes 6–8 The allocation length field specifies the maximum number
of bytes read by the initiator. If the 4-byte header is trans-
ferred, the transfer length includes the header. If the transfer
length is zero, no data is read; this is not an error.
)
H
Bits
5 4 3 2
1 1 1 1
0 0
Buffer ID (00 )
H
Buffer offset
Allocation length
0 0 0 0
, the initiator reads data from the
B
, the initiator reads data from the
B
). [Mode
H
1 0
0 0
Mode
0 0