Function Block Diagrams (FBD) is a graphical language that allows the user to program elements in "blocks". The blocks can then be wired together like electrical circuits. FBD is one of the languages supported by IEC 1131.
A function block diagram is a diagram which describes a function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines. Inputs and outputs of the blocks are wired together with connection lines, or links. Single lines may be used to connect two logical points of the diagram:
• An input variable and an input of a block.
• An output of a block and an input of another block.
• An output of a block and an output variable.
The connection is oriented, meaning that the line carries associated data from the left end to the right end. The left and right ends of the connection line must be of the same type. Multiple right connection is also called divergence can be used to broadcast information from its left end to each of its right ends. All ends of the connection must be of the same type.
The FBD supports:
• All IEC 61131-3 operators
• Multiple inputs / multiple outputs
• Set / Reset of outputs
• Bitmap graphics in library functions, function blocks and programs