Adding Loops

In this section, you will learn how to add and program loops inside a sequence.

This task shows you how to:

Before you begin: The Sequence Editor window is opened. Some usable IOs and tasks are already defined.
See Also
About the Sequencing Editor

Add a While-Do or a Do-While

The instructions defined in the loop are re-executed until the condition becomes false.

  • For a While-Do, the test on the condition is done at the beginning of the loop. That means that the set of instructions defined in the loop is never executed if the condition is false.
  • For a Do-While, the test on the condition is done at the end of the loop. That means that the set of instructions defined in the loop is executed at least once.
Note: In this procedure, we create a While-Do loop, but the same procedure can be used for a Do-While loop.

  1. To add a loop to a sequence, do one of the following:
    • Select Add a While Do in the toolbox and then click the blank page.
    • Drag Add a While Do to the blank page.


    • The loop instruction is added to the blank page.
    • The Loop dialog box appears.
  2. In the Type list, you can select the loop type: Do While or While Do.
  3. In the Condition box, enter a Boolean expression. For example, test an existing IO value.


    Note: The Goto label must be filled only if the instruction is a target of a Goto instruction.
  4. Click the check mark.


    Now, you can insert instructions inside the loop.

  5. To add an instruction in the loop, you have to drag-and-drop a new instruction in the middle of the loop.
    1. Select a task in the Usable window.
    2. Drag it over the vertical bar in the loop.

      Two marks appear at the center.



    3. Release the mouse.
      The Assignment dialog box appears.
    4. Click the check mark to close the dialog box.


    Task1 is executed until I1 is true.

Add a For Loop

You can re-execute a set of instructions for a specific number of times.

  1. To add a loop to a sequence, do one of the following:
    • Select Add a For in the toolbox and then click the blank page.
    • Drag Add a For to the blank page.


    • The loop instruction is added to the blank page.
    • The For dialog box appears.
  2. In the Type list, you can select the loop type: Up or Down.
  3. If required, you can change the index name, its upper and lower limit.
  4. Click the check mark.


    Now, you can add instructions inside the loop. Eventually, you can use the index inside the condition or to assign variables or IOs values.

  5. To add an instruction in the loop, you have to drag-and-drop a new instruction in the middle of the loop.
    1. Select a variable in the Usable window.
    2. Drag it over the vertical bar in the loop.

      Two marks appear at the center.



    3. Release the mouse.
      The Assignment dialog box appears.
    4. Enter a value in the assignment instruction.


    5. Click the check mark to close the dialog box.


    This new instruction will be executed 10 times.

Add a Break

You can exit a Do-While, a While-Do or a For loop using the Break instruction. For example, in the sequence above, the loop execution must be stopped if an emergency flag is raised.

  1. Select Add a Condition , then click the assignment instruction.


  2. Click Add Before.
    The Condition dialog box appears.
  3. Enter Emergency=true in the Condition box.
  4. Click the check mark.


  5. Drag the assignment instruction to the else branch of the condition instruction.


  6. Select Add a Break , then select the then branch of the condition instruction.


  7. Click the check mark.


If the Break instruction is executed, the next instruction to be executed is the one defined after the loop.

Tip: If you insert a break instruction outside a loop, it appears in red to show the error.