The LSNDE function block is used to trigger other logical events based on the falling transition of a logical signal. If the input value has changed from True to False since the block was last executed, the output of the block is set True. If the value has not changed from True to False, the block output is set False. The following figure shows how the LSNDE function block responds to a change in input:
Figure: LSNDE Function Block Execution Example
