Seagate Ultra 320 Bus phases resulting from Iureq changes, Wdtr negotiation or, Dtreq, Qasreq

Table 19 describes the bus phases resulting from IU_REQ changes.

Table 19: Bus phases resulting from IU_REQ changes

Initial	Modified	Causes	BUS phase following
	IU_REQ
IU_REQ			MESSAGE phases
	value
		a. PPR negotiation keeping IU_REQ set to zero;	COMMAND, DATA, STATUS,
0	0	b. WDTR negotiation; or	or BUS FREE phase
		c. SDTR negotiation
0	1	a. PPR negotiation setting IU_REQ to one	BUS FREE phase
		a. PPR negotiation setting IU_REQ to zero;	BUS FREE phase
1	0	b. WDTR negotiation; or
		c. SDTR negotiation
1	1	a. PPR negotiation keeping IU_REQ set to one	BUS FREE phase

2.12.8.2DT_REQ

The SCSI initiator port shall set DT_REQ to one to request that DT DATA phases be enabled. In response, the SCSI target port shall set DT_REQ to one if it agrees to use DT DATA phases or zero if it does not.

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

If DT_REQ is one, a DT data transfer agreement is in effect. If DT_REQ is zero, an asynchronous or ST data transfer agreement is in effect.

Table 20 defines valid combinations of DT_REQ and other fields.

2.12.8.3QAS_REQ

The SCSI initiator port shall set QAS_REQ to one to request that QAS be enabled. In response, the SCSI tar- get port shall set QAS_REQ to one if it supports QAS or zero if it does not.

The SCSI initiator port shall set QAS_REQ to zero to request that QAS be disabled. In response, the SCSI tar- get port shall set QAS_REQ to zero in the PPR IN message.

Table 12 defines valid combinations of QAS_REQ and other fields.

When an initiator port and a target port have negotiated with each other to enable QAS, either of the two ports may participate in QAS arbitrations when attempting to connect to the other port. When an initiator port and tar- get port have negotiated with each other to disable QAS, neither port shall participate in QAS arbitrations when attempting to connect to the other port.

When QAS and information unit transfers are both enabled for a connected SCSI target port, that SCSI target port may issue a QAS REQUEST message to release the bus after a DT DATA phase. When QAS is enabled for and information unit transfers are disabled for a connected SCSI target port, that SCSI target port shall not issue QAS REQUEST messages.

2.12.8.4HOLD_MCS

The SCSI initiator port shall set HOLD_MCS to one to indicate that the SCSI target port should hold any mar- gin control settings set with the margin control subpage of the port control mode page. In response, the SCSI target port shall set HOLD_MCS to one if it is capable of retaining the settings and zero if it is not.

The SCSI initiator port shall set HOLD_MCS to zero to indicate that the SCSI target port shall reset to their default values any margin control settings set with the margin control subpage of the port control mode page. In response, the SCSI target port shall set HOLD_MCS to zero.

46 Parallel SCSI Interface Product Manual, Rev. A )