LD as FBD

When working with LD it is very possible that you will want to use the result of the contact switch for controlling other POUs. On the one hand you can use the coils to put the result in a global variable which can then be used in another place. You can, however, also insert the possible call directly into your LD network. For this you introduce a POU with EN input.

Such POUs are completely normal operands, functions, programs, or function blocks which have an additional input which is labeled with EN. The EN input is always of the BOOL type and its meaning is: The POU with EN input is evaluated when EN has the value TRUE.

An EN POU is wired parallel to the coils, whereby the EN input is connected to the connecting line between the contacts and the coils. If the ON information is transmitted through this line, this POU will be evaluated completely normally.

Starting from such an EN POU, you can create networks similar to FBD.