Function block diagram

The function block diagram (FBD) is a graphical language for programmable logic controller design,[1] that can describe the function between input variables and output variables.

A function is described as a set of elementary blocks.

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: The connection is oriented, meaning that the line carries associated data from the left end to the right end.

The other supported languages are ladder logic, sequential function chart, structured text, and instruction list.