Seagate Medalist 2160WC (ST52160WC) Manual descargar pdf (Pagina 45)

3.0 Command set

The drives support a subset of the Group 0, Group 1 and Group 2

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). This field is ignored if an Identify Message is sent.

• The last byte is always zero.

3.2 Status byte

The drive terminates each command by sending the status byte (shown

below) to the initiator during the status phase before the command

complete message.

Bytes

Bits

76543210

Reserved

Status byte code

Rsvd

00 0

The

status byte

can be any of the following:

Good status.

The drive has successfully completed a command.

Check condition status.

The drive detected an error, an excep-

tion or an abnormal condition. In response, the initiator may issue

a Request Sense command to determine the nature of the condi-

tion.

Busy status.

The drive is busy and is unable to accept a command

from an initiator. The initiator retries the command later. The drive

returns a busy status if 1) the initiator has not sent the disconnect

message and tries to queue a command or 2) the initiator rejects

the disconnect message and the queue is not empty.

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Seagate Medalist 2160WC (ST52160WC) Manual Pagina 45