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IEC 1131


   What Is IEC 1131?
   Ladder Diagram
   Sequential Function Chart
   Function Block Diagram
   Structured Text
   Instruction Lists
 

What is IEC 1131?
Developed with the input of vendors, end-users and academics, IEC 1131 consists of five parts:
  1. General information
  2. Equipment and test requirements
  3. PLC programming languages
  4. User guidelines
  5. Communications
IEC 1131-3 is the international standard for programmable controller programming languages. As such, it specifies the syntax, semantics and display for the following suite of PLC programming languages: One of the primary benefits of the standard is that it allows multiple languages to be used within the same programmable controller. This allows the program developer to select the language best suited to each particular task. An analogy is that a mechanic wouldn't attempt to repair an automobile using only a screwdriver. The mechanic has a variety of tools available and chooses the best one for each task. Follow the above links for a description of each of the IEC 1131-3 languages and the types of applications they are best suited to.

"What is Rockwell Software's role in IEC 1131-3?"
Rockwell Software actively supports IEC 1131-3. Allen-Bradley Co. chairs the overall IEC 1131 standard and also the "part 3" section that defines the five programming languages. Also, Allen-Bradley/Rockwell Software are members of PLCopen.

"Are Rockwell Software's products "IEC 1131-3 compliant"?
RSI products already support three of the five languages. (IE Ladder Diagram, Sequential Function Chart and Structured Text.) Note: Vendors are not required to support all five languages in order to be IEC 1131-3 compliant.

Our most popular programmable controller architectures (PLC-5 and SLC-500) existed before the IEC work was completed. Therefore, we have taken a migration approach to addressing the standards where we already had an existing solution such as ladder logic. Newer languages, such as SFC and Structured Text (both of which are available with our PLC-5 products) are based on IEC 1131-3.

Structured Text:
ST is included with AI5 software (cat #s 9325-L5140, 9321-L5160, and 9323-L5300). ST is available as an add-on option (cat no. 9313-ST5) for 6200-PLC5. RSI's implementation of ST features the exclusive PowerText(TM) feature which provides real-time process information for debugging and application commissioning. RSI's ST is based on the standard, and is designed to maximize compliance.

Sequential Function Chart:
SFC is included with AI5 software (cat #s 9325-L5140, 9321-L5160 and 9323-L5300), WinLogic5 (cat nos. 9325-WL5140 and 9323-WL5300) and with 6200-PLC5 (9321-PLC5 and 9323-PLC5). RSI's implementation of SFC is one of the most compliant versions available from a control vendor. RSI also provides features which allow the SFC to very easily support some on the SP-88 concepts for batch application.

Ladder Diagram:
Our most popular programmable controller architectures (PLC-5 and SLC) existed before the IEC work was completed, so it's understandable that there are a few differences: The addressing structure is different (this can be minimized by using symbolic addressing), some instructions have a different mnemonic and the graphical representation of some instructions is different. However, you may be pleasantly surprised at how many IEC 1131-3 features are supported in RSLogix:

  1. Well-structured programs
    • Modular programs via multiple program files
    • User-definable subroutines and libraties
    • Code sectioning via Page Titles
  2. Full Execution Control
    • Different parts of a program can be executed at different times, at different rates and in parallel
    • RSLogix supports a rich set of predefined task models: MCP, JSR, STI, PII, etc
  3. Structured Configuration
    • Processor configuration is called a Controller in RSLogix. It has Memory, Programs, Procedures, task execution mechanisms, I/O Configuration, and a documentation database -- everything that the specification intended a PLC to have
  4. Symbolic programming
    • RSLogix goes beyond the standard by supporting freeform programming. It is not necessary to define the symbol before using it
  5. Global / Local data tables
    • RSLogix checks for scope violations during the verification process
  6. Strong data typing
    • SLC-500 and PLC-5 support a rich set of data types, from simple to complex
    • When creating data table elements, user can:
      • Give the Data Table a name and description for documentation purposes
      • Determine the size of the data table
      • Assign data scope to a program file
      • Assign protection to the Data Table via the Constants or Static Keywords
      • Assign the files as a Debug file for simulation purposes
Frequently Asked Questions:
"How can I get a copy of the IEC 1131-3 standard"?
Copies of the IEC 1131-3 standard may be purchased from:

American National Standards Institute, Inc. Customer Service Dept. 11 W. 42nd St., New York, NY 10036 Tel: (212) 642-4900 Fax: (212) 302-1486

Approximate cost is $300 US