PLC Programming

Project Components...
In FBD :
PLC_PRG
Action
Example for a possible call sequence for PLC_PRG:
LD 0
ST PRGexample.PAR (*Default setting for PAR is 0*)
CAL IL call (*ERG in IL call results in 1*)
CAL ST call (*ERG in ST call results in 2*)
CAL FBD call (*ERG in FBD call results in 3*)
If the variable PAR from the program PRGexample is initialized by a main program with 0, and then one after
the other programs are called with above named program calls, then the ERG result in the programs will have
the values 1, 2, and 3. If one exchanges the sequence of the calls, then the values of the given result
parameters also change in a corresponding fashion.
The PLC_PRG is a special predefined POU. Each project must contain this special program. This
POU is called exactly once per control cycle.
The first time the 'Project' 'Object Add' command is used after a new project has been created, the
default entry in the POU dialog box will be a POU named PLC_PRG of the program type. You should
not change this default setting!
If tasks have been defined, then the project may not contain any PLC_PRG, since in this case the
procedure sequence depends upon the task assignment.
Attention: Do not delete or rename the POU PLC_PRG (assuming you are not using a Task Configuration)!
PLC_PRG is generally the main program in a single task program.
Actions can be defined and assigned to function blocks and programmes ('Project' 'Add action'). The
action represents a further implementation which can be entirely created in another language as the
"normal" implementation. Each action is given a name.
An action works with the data from the function block or programme which it belongs to. The action
uses the same input/output variables and local variables as the "normal" implementation uses.
Example for an action of a function block
In the example given, calling up the function block Counter increases or decreases the output variable
"out", depending on the value of the input variable "in". Calling up the action Reset of the function
block sets the output variable to zero. The same variable "out" is written in both cases.
2-6 CoDeSys V2.3