Seagate Ultra 160 ユーザーズマニュアル

Parallel SCSI Interface Product Manual, Rev. A )                                       

   45

The protocol options fields affect the protocol used between the ports. The SCSI target port uses the protocol 
options bits to indicate to the SCSI initiator port if it agrees to enable the requested protocol options. Except for 
the PCOMP_EN bit, the SCSI target port shall not enable any protocol options that were not enabled in the 
negotiation message received from the SCSI initiator port.

Table 18 lists the protocol options bits.

The SCSI initiator port shall set IU_REQ to one in the PPR OUT message to request that information unit 
transfers be enabled. In response, the SCSI target port shall set its IU_REQ to one if it agrees to use informa-
tion unit transfers or zero if it does not.

The SCSI initiator port shall set IU_REQ to zero in the PPR OUT message to request that information unit 
transfers be disabled. In response, the SCSI target port shall set IU_REQ to zero in the PPR IN message.

If IU_REQ is one, an information unit transfer agreement is in effect. If IU_REQ is zero, an asynchronous, ST 
synchronous, or data group transfer agreement is in effect.

Table 20 defines valid combinations of IU_REQ and other fields.

Each SCSI target port shall maintain a bus free required flag. Each time a negotiation is successful that results 
in the IU_REQ bit being changed from the previous agreement (i.e., zero to one or one to zero) the SCSI target 
port shall set its bus free required flag to true. Any intermediate changes (e.g., from multiple successful PPR 
negotiations) shall be treated as changing IU_REQ even if the final value equals the initial value.

At the conclusion of the message phases, if the bus free required flag is set to true, the target port shall:

1) abort all tasks for the SCSI initiator port;

2) set the bus free required flag to false; and

3) go to a BUS FREE phase.

At the conclusion of the message phases, if the IU_REQ bit was changed as the result of a negotiation, the 
SCSI initiator device shall abort all tasks for the logical unit.

If the IU_REQ bit was set to one during a previous PPR negotiation and not changed by a subsequent PPR 
negotiation sequence, the target port shall not request that the task manager abort any tasks for that SCSI ini-
tiator port and shall go to the BUS FREE phase after responding with a PPR IN message.

Precompensation enable.

Retain training information.

Read streaming and read flow control enable.

Write flow control enable.

Hold margin control settings.

QAS enable request.

DT clocking enable request.

Information units enable request.