When referencing a parameter in another node, you can use the .CST field to verify communications with that parameter or node. The .CST field can be referenced in a CALC block or SFC expression. It is recommended that you verify external references to parameters in other nodes when using SFC pulse/assignment type actions. If such an external reference is used, you should make sure that it is bound (that is, a value is assigned) before continuing the step. This can be done using pulse action confirmation or a transition condition.
To verify such external references, the SFC expression could be written as follows:
The confirmation expression tests for the value of the .CST field being equal to 0 (connected) or less than 0 (never going to connect).
Subsequent expressions should test the .CST field of the individual external reference parameters to guide the SFC execution if the algorithm is going to handle missing or IGNORE connections.
To verify such external references, the CALC expression could be written as follows:
Set one of the OUT parameters equal to the .CST value of the remote node integrity or to a specific parameter such as RemoteNode1/OINTEG.CST or RemoteModule1/FB1/Parameter1.CST.
Use the value of the CALC OUT parameter to adjust your logic based on the remote node or module being unavailable.
Every time the module executes, the .CST value is updated with the current remote status.