Seagate Ultra 160 ユーザーズマニュアル

Parallel SCSI Interface Product Manual, Rev. A                                        

   87

The DISCONNECT message is sent from a SCSI target port to inform an initiator that the target plans to do a 
physical disconnect by releasing the BSY signal, and that a later physical reconnect is going to be required in 
order to complete the current task. This message shall not cause the initiator to save the data pointer. 

The target shall consider the message transmission to be successful when there is no attention condition on 
the DISCONNECT message.

After successfully sending this message, the target shall go to the BUS FREE phase by releasing the BSY sig-
nal. 

If an information unit transfer agreement is not in effect, any SCSI target port that breaks data transfers into 
one or more physical reconnections shall end each successful data transfer (except possibly the last) with a 
SAVE DATA POINTER—DISSCONNECT message sequence.

If an information unit transfer agreement is in effect, SCSI target ports shall not transmit a DISCONNECT mes-
sage.

This message may also be sent from an initiator to a target to instruct the target to do a physical disconnect. If 
this option is enabled and a DISCONNECT message is received, the target shall either:
a. if an information unit transfer agreement is not in effect—switch to MESSAGE IN phase, send the DISCON-

NECT message to the initiator (possibly preceded by SAVE DATA POINTER message), and then do a 
physical disconnect by releasing BSY; or

b. if an information unit transfer agreement is in effect, regardless of the QAS mode—do a physical disconnect 

by releasing BSY.

After releasing the BSY signal, the target shall not participate in another ARBITRATION phase for at least a 
disconnection delay or the time limit specified in the Physical Disconnect Time Limit

 

mode parameter (see 

Seagate SCSI Command Reference Manual, Part number 100293068.) whichever is greater. If this option is 
disabled or the target is not able to do a physical disconnect at the time when it receives the DISCONNECT 
message from the initiator, the target shall respond by sending a MESSAGE REJECT message to the initiator.

The IDENTIFY message (see Table 28) is sent by either the initiator or the target to establish an I_T_L nexus 
when information unit transfers are disabled.

The IDENTIFY bit shall be set to one to specify that this is an IDENTIFY message.

A DISCONNECT PRIVILEGE (DISCPRIV) bit of one specifies that the initiator has granted the target the privi-
lege of doing physical disconnects. A DISCPRIV bit of zero specifies that the target shall not do physical dis-
connects. This bit is not defined and shall be set to zero when an IDENTIFY message is sent by a target.

The target shall generate a BUSY status (see Section 3.8) for a task not granting a physical disconnect privi-
lege (DISCPRIV bit set to zero) in the IDENTIFY message if: 

a. there are any pending tasks, and 
b. the target determines that a physical reconnection of one or more pending tasks is required before the 

current task may be completed.

The LUN field specifies a logical unit number.

IDENTIFY

DISCPRIV

LUN