Examples: Execution when EN=TRUE

There is the same execution for a function. To illustrate this, here just the FBD-logic:

The execution is analogous to the one of the RS block: As input EN for ADD is set to value TRUE, output ENO is set to the value TRUE and the functionality of the ADD block is executed. Hence, the value 5 is assigned to the variables result1 and result2. As the assignments are executed, the variables Var7 and Var8 are also set to TRUE as well as the variables result3 and result4 are also set to value 5.

Examples: Execution when EN=FALSE

There is the same execution for a function. To illustrate this, here just the FBD-logic with the default behavior:

Again, the execution is analogous to the one of the RS block: As input EN for the call of ADD is now set to value FALSE, output ENO is set to the value FALSE and the functionality of the ADD block is not executed any longer. Due to EN=FALSE, the assignments from the output variables of the ADD block are not executed because they are located within the same network. The evidence for this is the assignment of output ENO of the ADD block to Var7: The value FALSE of output ENO is not assigned to the variable Var7 – so the last value TRUE is retained for Var7.
Note: As difference to a function block instance, the last return value of the function is not retained. Instead the return value of ADD is now 0, because it has been type-coded with the data type INT and 0 is the initial value of INT. The assignments from the return value are not executed as well (see the next examples for more explanations).
If the return value of ADD is 5 in your logi.CAD 3 version, you are using a c onfiguration where the variables and a return value of functions retain the last values assigned to them. And value 5 is the value that has been calculated at last.

In order to illustrate in detail that assignment from output variables are not executed due to EN=FALSE, the following values have been changed in the Values of Variables view:

• The value for Q1 of the function block instance RSa1 has been changed from TRUE to FALSE.
  

  

  
  Explanation of the execution: Although the value for Q1 of the RS block is now set to value FALSE, the variables Var2a and Var3a still have the value TRUE. Reason: Due to EN=FALSE of the RS block, the assignments from output variables are not executed because they are located within the same network. Mind that connectors and continuations are elements of the networks – although there is no graphical connection.
  Note: The following assignment from variable Var2a to Var5a and the one from Var3a to Var6a are executed again. This would become visible, if the values for Var2a and Var3a would be changed e.g. within the Values of Variables view.

• The value of the variable add1 (that is used as input for the ADD block) has been changed from 2 to 12.
  

  

  
  Again, the execution is analogous to the one of the RS block: Although add1 is now set to value 12, the variables result1 and result2 still have the value 5. Reason: Due to EN=FALSE of the ADD block, the assignments of the return value are not executed because they are located within the same network. Mind that connectors and continuations are elements of the networks – although there is no graphical connection.
  Note: The following assignment from variable result1 to result3 and the one from result2 to result4 are executed again. This would become visible, if the values for result1 and result2 would be changed e.g. within the Values of Variables view.

Examples: Forcing the assignments when EN=FALSE

In case of a block with EN=FALSE, you are able to force the assignments from the output variables anyway. Mind that the the corresponding example under "Examples: Execution when EN=FALSE" is the basis for the following illustrations.

If the block is a function block instance, there are 2 workarounds within the FBD-editor:

Due to EN=FALSE for the function block instances RS1b and RS1c, their output ENO is set to value FALSE. The value for Q1 of the corresponding function block instances has also been changed to FALSE – as seen in the previous examples. But in contrast to the previous examples, the assignments from the output variables are now executed because they are located within a different network (1st workaround) or they have been realized by using the MOVE block within the same network (2nd workaround).

It is not possible to enter output variables of functions within a value field. Reason: According to the IEC-standard, function do not store their state. Hence, there is only the following workaround for functions:

Due to EN=FALSE for ADD, the output ENO is set to value FALSE. The value for add1 has been changed to 12– as seen in the previous examples. But in contrast to the previous examples, the assignments from the return value are now executed because they have been realized by using the MOVE block within the same network. Mind that the variables result5 and result6 now have the value 0. Reason: The return value of ADD has been type-coded with the data type INT and 0 is the initial value of INT.

If the block is a function block instance, there is the following workaround within the ST-editor:

Due to EN=FALSE for RS1a and RS1b, their output ENO is set to value FALSE. The value for Q1 of the corresponding function block instances has been changed to FALSE – as done in the previous examples. But in contrast to RS1a, the assignments from the output variables of RS1b are executed because they are entered separately from the call.

If the block is a function, there is no workaround within the ST-editor. Reason: Function do not store their state. Subsquently, it is not possible to enter the output variables and the return value of the function separately from the call of the function.