RSLogix 5000 Programming Languages

RSLogix supports different programming languages. Using the right language for the right job can increase productivity, reduce complexity and maintenance costs. These languages are:

Ladder Diagram

Ladder Diagram (LD)

Ladder logic was created such that most engineers and technicians would easily understand it and be able to maintain it. This was achieved by making the language similar to relay circuits diagrams (PLCs were originally created to replace relay circuits).

• It has similar interface with RSLogix 5 and 500 which resembles the relay circuits.
• Ladder Logic is a sequential programming language that processes lines (called rungs) in sequential order until they are all run. It will then start from the first line again.
• Major improvement from PLC  5 and 500 in its ability to have aliases. This allows starting to code a program without having wiring diagrams of the plant. This can be done by simply giving aliases to various inputs and later define those aliases based on the wiring diagram when they are available.
• Allows easy use of arrays and structures.
• Allows editing the program while on-line with the PLC and in Run mode.

Function Block Diagram

Function Block Diagram (FBD)

• As the name implies this is a block diagram language where you can basically drop blocks and draw connections between them.
• Function Block Diagram is more of a graphical language than Ladder Logic.
• One of the main advantages of this language is that the engineer can easily program general math functions and trigonometry.
• The easy use of math functions in this language allows calculations of engineering concepts in feedback and control to optimize processes.
• Function Block Diagram is a popular language for automation jobs in Process Control such as oil industry or pharmaceutical.
• Allows editing the program while on-line with the PLC and in Run mode.

Sequential Function Chart (SFC)

• This is also a graphical programming language.
• It is mostly used to create machine / batch sequences.
• Allows transitions between branches.
• Sequential function chart is easier to read and understand which also makes it easier to maintain on job sites.
• It allows importing routines from LD, FBD, or from within SFC enviroment.
• Allows editing the program while on-line with the PLC and in Run mode.

Structured Text

Structured Text (ST)

• This language is closest to a typical computer programming language (Visual Basic, C++, etc).
• Structured text is a text based editor which means no blocks or graphics or arrows.
• Commands such as If/Then, Case, Do/While, and Do/Until are common commands used in this language.
• Most LD and FBD instructions are supported and routines from all other RSLogix 5000 languages can be called if needed.
• Allows editing the program while on-line with the PLC and in Run mode.

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