Echelon i.LON 100 e2 Internet Server - Manual (Page 22)

i. LON 100 Internet Server Programmer’s Reference 3-5
Property Description
0 or 1. If you assign the default value 1 to the
property, the change you make to the data
point value will be propagated over the network. If you assign
value 0 to this property, the change will be made in the
i. LON
100 Data Server, but not over the network.
This may be useful if you are writing to different fields of a
structure with separate calls to DataPointWrite, and do not
want to update the structure over the network until all of its
fields have been written to.
3.3.1 Data Point Values and Priority Levels
As described in the previous section, the DataPointWrite function requires you to specify a
priority level when writing to a data point. In order to successfully update the value of the
data point, you must specify a higher priority level than the one used by the last application
to write to the data point.
For example, consider a scenario where a SOAP application uses the DataPointWrite
function to write to the value of a data point called NVL_nvoValue. Assume that the last
application to write to the value of NVL_nvoValue used priority level 75 when it updated the
data point. In that case, the current application must use a priority value between 0 and 75
to successfully write a new value to the data point.
Data point priority levels allow you to give some applications precedence over others when
more than one application might attempt to update the same data point. Table 4 depicts a
series of events where various applications write to the value of a single data point. For each
event, the priority level used is listed, as well as a description of whether or not the update
was successful, and why. This should help you understand how you can use data point
priority levels to determine which applications will be given precedence when updating the
value of a data point.
Table 4 Data Point Priority Levels and Values
Event Priority Level
Assigned
Result of Operation
Power-Up 255 The value of the data point is updated
successfully.
Event Scheduler Updates
Data Point
240 The value of the data point is updated
successfully, as the priority used by the Event
Scheduler is greater than that assigned to the data
point during power-up.
Custom Application
Invokes DataPointWrite
75
The value of the data point is updated
successfully, as the priority used in the call to
DataPointWrite is greater than that assigned to
the data point by the Event Scheduler.
Event Scheduler Updates
Data Point 240 The value of the data point is not updated
successfully, as the priority used by the Event
Scheduler is less than that used by the last
application to update the data point.