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Structuring with SFC
do's & don'ts
V1.0 Official Release


PLCopen Safety
Part 1
Version 2.0 now released


Information Model
V1.01.09 RfC


PLCopen starts
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on Industry 4.0










Conformity Level


With the broad range of application areas for IEC 61131-3 not all implementations use exactly the same data types. To accompany this, the certification according to Conformity Level, CL, implies that the supplier of a PSE selects the data types supported by his product matching his conformity statement. All supported IEC features are tested. This means that although the test is a Yes/No test (compliant or non-compliant), there can be differences between two certified products. These differences can influence the reusability of user derived function blocks.

The total number of data types as specified in the Standard amounts to 26 (table 10 and 12 of the Standard). These range from simple digital Yes/No (BOOL) to potential complex structures Therefore, CL has 26 options: data type supported or not-supported. Only the supported data types are used for testing.

In addition Reusability Level, RL, is dedicated to making the programming units functions and function blocks reusable on a different PSE. This is done via exchange in a plain textual format of the language Structured Text, ST. For representation in other languages, a conversion tool to or from ST can be included. This is a major, but natural, contribution of PLCopen to the IEC 61131-3 standard.

The export/import format contains only common elements defined by the IEC, but no PLCopen specific elements as headers. Each RL file contains only one FUNCTION_BLOCK...END_ FUNCTION_BLOCK or TYPE...END_TYPE section.

Reusability on a different PSE is guaranteed for the matching supported set of data types and the corresponding IEC functionality. Users therefore have to check if the targeted systems include the data types intended to be used. The amount of supported data types is listed on the certificate, as issued by PLCopen, and the supplier on your request should make a full list available. The reusability is focused to the standard functionality as defined within the Standard. For supplier dependent functions and function blocks there may be no equivalent on the receiving side, meaning that it will not work on the other system.

Historically there exists a lower class called Base Level, defining a core kernel per language of the standard. Although rather restricted, it is feasible to develop applications based on it. Base Level provides an entrance level for the suppliers, showing their commitment to the standard. For the users it provides a normalized interpretation of the standard, especially important if they have to work with systems of different vendors.

Detailed specifications of most of the IEC 61131-3 languages are already finished. Work is in progress for the remaining languages. The conformance test procedure and the accreditation procedure for test laboratories have been established. Independent test laboratories have been accredited and an increasing number of products have been certified. View the complete list of certified products.