Command Set; Command Descriptor Block - Seagate ST3285N Product Manual

ST3655 Family SCSI Drives Product Manual, Rev. A

3.0 Command set

The drive supports a subset of the Group 0 and Group 1 standard SCSI
commands. The commands are described in this section.

3.1 Command descriptor block

The initiator makes a request to the drive by sending a command
descriptor block (CDB) to the drive. Each CDB has the following common
characteristics:
• Byte 0 always contains the operation code.
• The three most significant bits (bits 7–5) of byte 1 contain the logical
unit number (LUN), which is always zero.
• If the link bit is zero, the flag bit must be zero; otherwise, the drive
returns a check condition status. If the link bit is one and the drive
completes the command without error, the flag bit specifies which
message the drive returns to the initiator. If the flag bit is zero, the
drive sends the linked command complete message. If the flag bit is
one, the drive sends the linked command complete with flag message.
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