2 dt_req, 3 qas_req, 4 hold_mcs – Seagate Ultra 320 User Manual
Page 60
46
Parallel SCSI Interface Product Manual, Rev. A )
Table 19 describes the bus phases resulting from IU_REQ changes.
2.12.8.2
DT_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.
2.12.8.3
QAS_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.
2.12.8.4
HOLD_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.
Table 19:
Bus phases resulting from IU_REQ changes
Initial
IU_REQ
Modified
IU_REQ
value
Causes
BUS phase following
MESSAGE phases
0
0
a. PPR negotiation keeping IU_REQ set to zero;
b. WDTR negotiation; or
c. SDTR negotiation
COMMAND, DATA, STATUS,
or BUS FREE phase
0
1
a. PPR negotiation setting IU_REQ to one
BUS FREE phase
1
0
a. PPR negotiation setting IU_REQ to zero;
b. WDTR negotiation; or
c. SDTR negotiation
BUS FREE phase
1
1
a. PPR negotiation keeping IU_REQ set to one
BUS FREE phase