Function Block Diagram (FBD)

A function block diagram is a data flow between constant expressions or variables and operations represented by rectangular blocks.

• Operations can be basic operations, function calls, or function block calls.
• See Use ST Expressions in Graphic Language.
• The name of the operation or function, or the type of function block is written within the block rectangle.
• With a function block call, the name of the called instance is written in the header of the block rectangle.

Example

Data Flow

• The data flow represents values of any data type.
  • All connections must be from input and outputs points having the same data type.
• With a Boolean connection, use a connection link terminated by a small circle.
  • This indicates a Boolean negation of the data flow.
  • See also see "Draw FBD Connection Lines" on page 1.

• The data flow must be understood from the left to the right and from the top to the bottom.
  • It is possible to use labels and jumps to change the default data flow execution.

FFLD Symbols

FFLD symbols can also be entered in FBD diagrams and linked to FBD objects.

• See these sections for information about components of the FFLD language:
  • FFLD Coils
  • FFLD Contacts
  • Power Rails
• Special vertical lines are available in FBD language for representing the merging of FFLD parallel lines.
  • Such vertical lines represent a OR operation between the connected inputs.

Figure 1: Example: OR Vertical Line used in an FBD Diagram

See Also

• FBD Editor Keyboard Shortcuts
• Function Block Diagram (FBD) Editor
• Using the FBD Toolbar