IEC 1131 Function Block Diagram Overview
Like SFC, FBD is a graphical language that allows programming in other languages (ladder, instruction list, or structured text) to be nested within the FBD. In FBD, program elements appear as blocks which are "wired" together in a manner resembling a circuit diagram. FBD is most useful in those applications involving a high degree of information/data flow between control components, such as process control.
