Introduction
FFB pins (inputs and outputs) of the data type BOOL can be negated.
Negated pins are identified with a circle symbol:

NOTE: Negated pins must be connected with a graphical
link or a variable. Open negated pins are not allowed.
Negating an FFB pin
FFB pins can be negated in the following ways:
Select the pin to be negated and execute the menu command
in the shortcut menu (right-click).or
Launch the Inversion tool by clicking on the
icon, then click on the pin to be negated.