Define the PLC Cycle

The cycle specification defines the number of cycles between successive executions of the programs.

Procedure

1. In the Project Explorer, expand the PLC node.
2. Right-click on Programs and select Cycle. (Figure 1)



Figure 1: PLC > Programs > Cycle

The Cycle dialog box opens. (Figure 2)



Figure 2: Cycle dialog box

The Cycle dialog box is used to:

• Change the Period and Phase parameters.
• Configure the programs priority into the Virtual Machine.

Column	Description
Name	List of PLC programs grouped together by priority level. The priority defines the order of execution. The SFC programs have a specific section as they must be grouped together. High Priority means executed before SFC. Low Priority means executed after SFC.
Check box	Enables or disables the execution of the corresponding program.
Period	Defines how many cycles are set between two executions of the program. You can define various sampling periods for programs of the application. The default period is 1 (i.e., the program is executed on each cycle). Using a slower period for some programs is an easy way to give higher priority to some other programs.
Phase	Defines an offset that enables you to dispatch slow programs among few cycles. The goal of postponing the program execution is to reduce execution peak loads. Examples A program with period=2 and Phase=1 is executed each even cycle. A program with period=2 and Phase=0 is executed each odd cycle

In the High and Normal Priority sections, adjust the order of the programs with a drag-and-drop operation according to the expected sequence. In each section, the program on the top is executed first.

Select the program to set with a higher priority, then drag and drop it to the relevant priority level. (Figure 3)

Figure 3: Change Priorities by Defining the Cycle

If all programs are with a Period set to 1, the KAS-IDE is more loaded. The choice of the Period for the programs gives you the possibility to distribute the load of the application.

See Also

• Tasking Model / Scheduling
• Order of Program Execution

Specify the Duration of a Cycle

This parameter is defined in EtherCAT Master Settings tab.

Ensure Variables are Exported

Program Organization Units (POUs) containing variables (see Map Variables to HMI) must be compiled for the variable to be exported.

Example

In the Figure 7 images, a POU (UntitledST) has two variables: NewVar and NewVar1.

1. Only NewVar1 is set to be exported (Figure 4).
2. The POU, however, is not set to be executed in the Cycle dialog box (Figure 5).
3. This causes a compile error (Figure 6).

Figure 4: NewVar1 is set to be exported

Figure 5: POU is not set to be executed

Figure 6: Compile error

Figure 7: Examples of a variable not being exported and the resulting compile error.