Is -p- a short message number in Mitsubishi PLC programming? -f- stands for long signal? If you don't understand these two usages, it makes sense.

F is the falling edge.

Edge signals are usually used. For example, the count c is only recorded once when the signal changes from 0 to 1, and it is+1 until1or 0.

For example, the purpose of initialization reset is to reset this bit, so it does not need to be reset all the time, so it is triggered by the edge signal and does not affect the subsequent operation.