Draw FBD connection lines

Press this button before inserting a new line.


  • As shown below, the editor enables you to terminate a connection line with a Boolean negation represented by a small circle:

    (* use of a negated link: Q is IN1 AND NOT IN2 *)
    Not FBD
    To set or remove the Boolean negation, select the line and press the Spacebar.

Connection lines must always be drawn in the direction of the data flow: from an output pin to an input pin. The FBDClosed "Function block diagram" A function block diagram describes a function between input variables and output variables. A function is described as a set of elementary blocks editor automatically selects the best routing for the new line. Connection lines indicate a data flow between the following possible objects:


  • Line is colored in red when the two linked items are not the same type.

Block: Refer to the help on the block for the description of its input and output pins, and the expected data types for the coherence of the diagram. 

Variable: A variable can be connected on its right-hand side (to initiate a flow) or on their left-hand side to force the variable, if it is not "read only". The flow must fit the data type of the variable. 

Jump: a jump must be connected on its left-hand side to a Boolean data flow. 

Left power rail: Left power rails represent a TRUE state and can be connected to a non limited number of objects on their right-hand side. 

Contact: A contact must be connected on its left-hand side and on its right-hand side to Boolean data flows. 

"OR" rail: Such a rail collects several Boolean data flows for an "OR" operation, in order to insert parallel contacts, as in Ladder Diagrams. It may have several connections on its left-hand side and on its right-hand side. All connected data flows must be Boolean. 

Coil: A coil must be connected on its left-hand side to a Boolean data flow. It is not mandatory that a coil be connected on its right-hand side. 

Right power rail: A right power rail is an element of the FFLD language, and is commonly used for terminating Boolean data flows. It has an unlimited number of connections on its left-hand side. It is not mandatory to connect coils to power rails.


  • Connection lines automatically move and follow FBD elements (1) and you can also manually specify the corners. Simply double-click on the line to show a "handle" (2) which can be repositioned (3).