132 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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5.2.1.4
Read Command (08h)
Table 5.2.1-9. Read Command
Bit
7
6
5
4
3
2
1
0
Byte(s)
0
0
0
0
0
1
0
0
0
1
Logical Unit No.[1]
Logical Block Address (MSB)
[2]
0
0
0
2
Logical Block Address
3
Logical Block Address (LSB)
4
Transfer Length
[3]
5
0
0
0
0
0
0 Flag Link [4]
The Read Command (Table 5.2.1-9) requests that the disc drive transfer data to the initiator.
Notes.
[1] In the CDB the LUN must be zero.
[2] The Logical Block Address specifies that logical block at which the read operation shall begin.
[3] The Transfer Length specifies the number of contiguous logical blocks of data to be transferred. A Trans-
fer Length of zero indicates that 256 logical blocks shall be transferred. Any other value indicates the
number of logical blocks that shall be transferred.
[4] See “Control Byte” paragraph 4.2.6.
The data value most recently written in the addressed logical block shall be returned.
Read data transfers with the initiator do not begin until at least one full sector of data is available in the disc
drive data buffer. For multiple sector reads, the transfer of data continues until the number of blocks specified
in byte 4 of the CDB has been read and transferred or until an unrecoverable error is detected.
Data transfer could stop if the option to stop on recovered error is selected.
For systems that support disconnection, the disc drive disconnects when a valid Read command is received.
The disc drive reconnects depending on the value of the Buffer Full Ratio Set in Page 2 of the Mode Select
Data (see Section 5.2.1.7). After data transfer has been initiated with an initiator, the disc drive does not
disconnect unless an internal error recovery procedure is required or the data transfer to an initiator is inter-
rupted for more than 1 millisecond.
The initiator must accept all data presented to the initiator after sending this command until the disc drive
sends Completion Status during a Status phase. (Note the disc drive may disconnect and reconnect while
executing this command and the initiator may prematurely terminate this command by creating the Reset
condition or by sending an Abort, Abort Tag, Clear Queue or Bus Device Reset message).
