Ladder Diagram and Function Block Diagram are programming languages that represent a program by means of standardized graphical symbols for programming elements.
Programming elements in LD include a power rail, contacts, coils, input and output variables, functions, function blocks, jumps and returns, horizontal and vertical lines.
FBD uses similar programming elements but does not have a power rail, contacts, and coils. In this section, examples and descriptions refer to LD unless stated otherwise.
Example for LD
Three networks programmed in ladder diagram:
Example for FBD
Two networks programmed in function block diagram:
The program is displayed in the programming window with POU header and POU body. The POU body is divided into networks. Each network has a network header containing the network number and information, e.g. labels or breakpoints.
Operation link results will be lost from one network to another. Therefore, each result required for further use must be saved (in a variable) before another network is processed.
To open the online help for a function, function block, or operator, select the object in the POU body and press <F1>.
There is a maximum number of 160 elements per network. When drawing lines, make sure to draw them as one element, because each line fragment is counted as an element.