FFLD Coils

Coils are basic graphic elements of the FFLD language. A coil is associated with a Boolean variable which is displayed above the graphic symbol. A coil performs a change of the associated variable according to the flow on its left-hand side.

Below are the six possible coil symbols:

Coils Description
boolVariable

   -( )- 		Normal: the associated variable is forced to the value of the flow on the left of the coil.
boolVariable

   -(/)- 		Negated: the associated variable is forced to the negation of the flow on the left of the coil.
boolVariable

   -(S)-

Set: the associated variable is forced to TRUE if the flow on the left is TRUE. (no action if the flow is FALSE)

  • Power Flow on left is TRUE:
  • The horizontal wires on either side of the (S) are red
  • The variable and the (S) are red
  • Power Flow on left is FALSE and the (S) variable is Energized (ON)
  • The horizontal lines on either sided of (S) are black
  • The variable and the (S) are red
  • In all other cases:
  • The horizontal wires are black
  • The variable and the (S) are black
boolVariable

   -(R)-

Reset: the associated variable is forced to FALSE if the flow on the left is TRUE. (no action if the rung state is FALSE)

  • Power Flow on left is TRUE:
  • The horizontal lines are red
  • The variable above (R) is black
  • The R and the circle around the R are black
  • Power Flow on left is FALSE and variable above reset coil is NOT Energized (OFF)
  • The horizontal lines are black
  • The variable above (R) is black
  • The R and the circle around the R are black
  • Power Flow on left is FALSE and variable above reset coil is Energized (ON)
  • The horizontal lines are black
  • The variable above (R) is red
  • The R and the circle around the R are red
boolVariable

   -(P)- 		Positive transition: the associated variable is forced to TRUE if the flow on the left changes from FALSE to TRUE(and forced to FALSE in all other cases)
boolVariable

   -(N)- 		Negative transition: the associated variable is forced to TRUE if the flow on the left changes from TRUE to FALSE(and forced to FALSE in all other cases)

  • When a contact or coil is selected, you can press the Spacebar to change its type (normal, negated...)
    When your application is running, you can select a contact and press the Spacebar to swap its value between TRUE and FALSE



  • Although coils are commonly put at the end, the rung can be continued after a coil. The flow is never changed by a coil symbol.