EcoStruxure Machine Expert - Safety supports the graphical IEC 61131-3 programming languages Function Block Diagram (FBD) and Ladder Diagram (LD) for developing code. FBD and LD can be mixed, i.e., their objects can be used together in one code worksheet, networks of both languages can be connected.
In addition, the textual IEC 61131-3 programming language Structured Text (ST) is supported.
The IEC 61131-3 standard defines the syntax of these programming languages, specifies their representation and describes the elements and objects which can be used in the languages.
Function Block Diagram (FBD)
Code programmed in the graphical language FBD is composed of functions and function blocks which are connected to each other or to variables or literals using lines. These lines can also be connected to each other. In FBD networks, it is not possible to connect outputs with outputs. Due to safety requirements it is furthermore not allowed to program explicit feedbacks.
The set of connected objects is called FBD network. Comments can be inserted to improve the comprehensibility of the code.
Ladder Diagram (LD)
Code programmed in the graphic language LD is composed of contacts and coils. According to IEC 61131-3, different types of contacts and coils can be used. Contacts lead (according to their type) the power from the left to the right. Coils store the incoming value. Both contacts and coils must be assigned to Boolean variables.
Contacts and coils are connected with lines and they are bounded on the left and on the right by power rails. The state of the left power rail is considered ON all the time. 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 must at least contain one coil, a left and a right power rail. Comments can be inserted to improve the comprehensibility of the code.
Structured Text (ST)
Code programmed in the textual language ST consists of statements and expressions. Each instruction must be terminated with a semicolon. To improve code readability, start each instruction in a new code line.
The operators have to be applied to the operands in the way that the operator with the highest precedence is followed by the operators with the next lower precedence. Although the compiler resolves the correct precedence of several operators used together in one statement, place parentheses in order to emphasize the precedence of the operator, thus improving code readability.
Operands in ST can be literals, variables, or names of functions. Operands are used together with operators in expressions.
Comments can be inserted to improve the comprehensibility of the code.
Further Information
Description of ST language elements (statements and expressions) .
