Cicode is pre-empted and executed on an instruction-by-instruction basis. This means that execution of a simple unnested Cicode thread can only switch to another thread after the current Cicode instruction has completed execution.
CitectVBA code is pre-empted and executed on a line-by-line basis (as opposed to an instruction-by-instruction basis), and pre-empting can only occur after the current line has completed execution.
Each line of CitectVBA script is handled as a separate thread in CitectSCADA. Therefore multiple procedures placed on one line may not complete before another subsequent thread is processed in a multithreading environment. This could cause unpredictable results and consequences, including data invalidation and corruption.
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UNINTENDED EQUIPMENT OPERATION
Failure to follow these instructions can result in death, serious injury, or equipment damage. |
If, for example, you were reading or setting some variable or point in a multi-statement thread, and further processing that data in a later thread,that data might become invalid or incorrect. For this reason, you should separate every statement onto separate lines in CitectVBA.
For example, it is better to write:
A = Motor1.speed() + Motor4.speed() + Motor5.speed()
as
A = Motor1.speed()
A = A + Motor4.speed()
A = A + Motor5.speed()
in situations where the method speed()may take a long time to execute.
In the first example above, the CitectVBA thread executes for three times longer before it can be pre-empted than in the latter example.
Note: This does not apply to Cicode because the Cicode engine can pre-empt aggregated code.
See Also
Accessing Cicode Tags with CitectVBA
Using CitectVBA in CitectSCADA Command or Expression fields