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Function Block Diagram - FBD
A code body programmed in the graphical language FBD is composed of functions and function blocks which are connected with each other or with variables using lines. These lines can also be connected with each other. In FBD networks it is not possible to connect outputs with outputs.

The set of connected objects is called FBD network.

Connectors can be used in case of large networks for better structuring the elements in the worksheet. Connectors replace connection lines.

Jumps can be used to jump to a label in the current worksheet.

Returns can be inserted to go back to the calling POU.

Ladder Diagram - LD
A code body programmed in the graphic language LD is composed of contacts and coils. According to IEC 1131-3 different types of contacts and coils can be used. The contacts lead according to their type the power from the left to the right. Coils store the incoming value to Boolean variables.

These contacts and coils are connected with lines and are bounded on the left and on the right with power rails. The state of the left power rail is considered ON all the time. The right rail is optional.

In addition to the serial connections of contacts and coils parallel branches can be created. Parallel branches are also called wired-ORs.

The set of connected objects is called LD network. Every LD network shall at least contain one coil and a left power rail.

Connectors can be used in case of large networks for better structuring the elements in the worksheet. Connectors replace connection lines.

Jumps can be used to jump to a label in the current worksheet.

Returns can be inserted to go back to the calling POU.

Variables in LD code bodies are always Boolean variables. While inserting contacts or coils the variable name can be entered. The variable name is displayed above the contact or coil in the worksheet.

Sequential Function Chart - SFC
A code body programmed in the graphic language SFC is composed of steps and transitions which are connected with directed links.

One or several action blocks can be associated to a step. While the step is active the associated action is executed according to the action qualifier. The action can be a Boolean variable. It is also possible to edit the code to be executed in an additional code body named detail. In this case the name of the code body worksheet has to be used as the name for the action.

A transition represents the condition in which the process passes from one step to another. If a transition becomes TRUE the preceeding step is executed once again and the succeeding step becomes active. The transition can be either a Boolean variable or a directly connected Boolean expression in FBD or LD. It is also possible to edit the code to be executed in an additional code body named detail. In this case the name of the code body worksheet has to be inserted at the transition.

The set of connected objects is called SFC network. A SFC network must have always one initial step which is the first step to be executed when the POU is called.

Simultaneous branches or alternative branches can be inserted in the SFC network.

Real-Time Operating System 实时操作系统(RTOS).