Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 79)

5
●
Defining Data Points
●
●
●
●
●
79
so that the value will remain fresh. Or create another data point using the
same address and make it a scheduled data point so that the Transaction
Control Manager service or FactoryTalk Transaction Manager service can
then request it as needed.
The unscheduled trigger is considered to be fresh when it starts a transaction.
If the Transaction Control Manager service or FactoryTalk Transaction
Manager service starts a transaction and determines it has already requested
a data point but not yet received a reply, it will not request the data point
again. Rather, it uses the same value for both transactions when the value is
received.
D ATA R ETRIEVAL T IMEOUT
The data retrieval timeout is measured from the start of the transaction until
the data point arrives. If there is any latency in the communications between
any of the following, the data point timeout may be affected:
 Transaction Control Manager service and the data server.
 FactoryTalk Transaction Manager service and the control connector,
and the control connector and the data server.
An example of this type of latency is using a device-scheduled data point in
FactoryTalk. In this case, the Transaction Control Manager service or
FactoryTalk Transaction Manager service requests the data point from the
control connector. The control connector then sends notification to the
FactoryTalk Live Data server. The FactoryTalk Live Data server sends a
read request to the controller, which in turn returns the data value. The
FactoryTalk Live Data server sends the value to the control connector,
which sends it to the Transaction Control Manager service or FactoryTalk
Transaction Manager service. If the data point is not returned by the time
specified in the data retrieval parameter, the rules of substitution are applied.