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 Draw FBD Connection Lines.

• 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 "Free Form Ladder Diagram" 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 6-66: Example: OR Vertical Line used in an FBD Diagram

See Also

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