The Bi-directional Edge Trigger function block examines the input value, compares it to the previous input value, and sets the output True for one scan period when the input has changed. Otherwise, the output is False. The status of the output value is set to the status of the input value.
The following figure illustrates how the Bi-directional Edge Trigger function block responds to a change in input:
Figure: Bi-directional Edge Trigger function block execution example
