Read Buffer Command (3Ch) - Seagate SCSI Interface Product Manual

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5.20

Read Buffer command (3Ch)

The Read Buffer command is used in conjunction with the Write Buffer command as a diagnostic function for
testing drive memory and the SCSI bus integrity. This command shall not alter the medium. Command format
is shown in Table 120.
Table 120: Read Buffer command (3Ch)
Bit 7
Byte
0 0
1 0
Logical Unit Number [1]
2 Buffer ID [5]
3 (MSB)
4
5
6 (MSB)
7
8
9 0
Notes.
[1] The Logical Unit Number must be zero.
[2] Read Buffer Mode field. The interpretation of data bits 0-3 is given in the following table and referenced
sections.
DB3 DB2 DB1
0 0 0
0 0 1
0 0 1
0 1 0
0 1 0
0 1 1
0 1 1
1 0 1
1 0 1
1 0 0
1 0 0
1 1 0
: : :
1 1 1
[3] Drive specific size also depends on whether cache is enabled as shown in Table 95 (RCD = 0) or not
(RCD = 1). See individual drive's Product Manual, Volume 1, under list of SCSI commands supported.
[4] See "Control byte," paragraph 4.2.6.
[5] Not implemented by drives supported by this manual. Must be zero.
[6] The Read data from echo buffer mode and Echo buffer descriptor mode do not apply to drives marketed
before the release of Rev. J of this manual. Drives marketed after Rev. J may or may not support these
two modes. See individual drive's Product Manual, Volume 1, for declaration of support.
6 5
0 1
0 0
Reserved
Allocation Length [3]
0 0
DB0 Mode definition
0 Read combined descriptor header and data (Section 5.20.1)
0 Read data (Section 5.20.2)
1 Read descriptor (Section 5.20.3)
0 Reserved
1 Reserved
0 Reserved
1 Reserved
0 Read data from echo buffer (Section 5.20.4) [6]
1 Echo buffer descriptor mode (Section 5.20.5) [6]
0 Reserved
1 Reserved
0 Reserved
: Reserved
1 Reserved
SCSI Interface Product Manual, Rev. J
4 3
1 1
0
Buffer Offset [5]
0 0
2 1
1 0
Mode [2] [6]
(LSB)
(LSB)
0 Flag [4] Link [4]
0
0