PLC programming conventions
In the world of programming languages, there are several conventions that are observed depending on the tooling, focus and origin of the programming language, as well as the industry in which the application is used.
Based on the generally accepted programming guidelines (such as the MISRA C++ 2008 guidelines[...], the Java code conventions, the C# programming guide or PLCopen), the following section contains further programming information, which facilitates the creation of optimum, functional PLC program code.
Follow PLC programming conventions to achieve the following benefits:
- uniform structure of the PLC programs
- consistent naming of objects, variables and instances
- easy readability and intuitive comprehensibility of code and especially of the interfaces of function blocks, methods and functions
- simplified development, use and maintenance of the programs
- increased code quality through the systematic and early avoidance of error sources
New Beckhoff TwinCAT 3 PLC libraries, program samples and applications follow these "TwinCAT 3 PLC programming conventions".
Exceptions:
- Tc2_MC2_xxx libraries comply with the PLCopen programming convention.
- Tc2_xxx libraries comply with the original TwinCAT 2 libraries.
- Industry-specific libraries are based on the respective industry standard.
- Function blocks from the IEC61131 standard, which are part of the Tc2_Standard library.
Classification
The PLC programming conventions are divided into the following chapters:
Within each chapter there are subchapters, which in turn contain a listing of topics.
The individual topics are classified as
- regulation, marked with [++], or as a
- recommendation, marked with [+].
You must implement topics classified as regulations. Recommendations should always be implemented, if possible, because they are advisable for several reasons.
Static code analysis
To reduce the risk of runtime errors, the code should at least be checked using the free variant of static code analysis (Static Analysis Light). This is included from TwinCAT 3.1 Build 4018 and contains a minimal scope for code review. With the help of the full range of functions of TE1200 PLC Static Analysis, a more detailed review of the programming conventions is also possible (see the following section).
Verification of programming conventions with the help of TE1200 PLC Static Analysis
TE1200 PLC Static Analysis offers the possibility of versatile checks of PLC program code. With the help of these functionalities, compliance with many regulations, recommendations and naming conventions of the PLC programming conventions can be checked.
Subchapter Programming
Where available, each regulation/recommendation is accompanied by the corresponding rule from Static Analysis that can be used to verify compliance with the regulation/recommendation.
See also:
- Subchapter Programming
- Functionality Rules from TE1200 PLC Static Analysis
Subchapter Naming conventions
If available, the ID of the Static Analysis configuration field is given for each naming convention, in which the respective recommended name prefix must be entered. This allows most of the recommended prefixes for POUs, DUTs, variables and instances to be checked by Static Analysis.
See also:
- Subchapter Naming conventions
- Functionality Naming conventions from TE1200 PLC Static Analysis
Pragmas and attributes
Also note the possibility to disable Static Analysis rules and naming conventions locally via pragma or attribute for checked locations where a specific rule/naming convention should no longer be reported (see also: chapter Pragmas and Attributes in TE1200 PLC Static Analysis). Ideally, you should comment on local deactivation with an appropriate explanation.
Download Static Analysis configuration file
1) Regulations and recommendations
The following link allows you to download a pre-built Static Analysis configuration file with the regulations [++] and recommendations [+] of the programming conventions enabled as rules. A violation of a regulation is output as an error after execution of the Static Analysis, a violation of a recommendation is classified as a warning.
2) Regulations, recommendations and naming conventions
The following link allows you to download a pre-built Static Analysis configuration file with the regulations [++], recommendations [+] and naming conventions of the programming conventions enabled as rules. A violation of a regulation or a naming convention is output as an error after execution of the Static Analysis, a violation of a recommendation is classified as a warning.
More rules
In addition to the rules that are explicitly mentioned within the following programming conventions, the TE1200 provides many other useful rules that can be used to detect careless errors or general programming errors at an early stage. These include, but are not limited to, the following rules.
- SA0008: Check subrange types
- SA0041: Possibly loop-invariant code
- SA0044: Declarations with reference to interface
- SA0056: Constant out of valid range
- SA0059: Comparison operations always returning TRUE or FALSE
- SA0060: Zero used as invalid operand
- SA0062: Using TRUE and FALSE in expressions
- SA0140: Statements commented out