TABLE OF CONTENTS Keywords are special words [1] that are used within the IEC languages to define different constructs or the start and end of particular software elements. For example, a function type definition is framed with keywords FUNCTION and END_FUNCTION.
A full list of keywords used by the IEC 1131-3 standard is given in Appendix 1. As a general rule, the use of identifiers that may be confused with language keywords should be avoided even though many language compilers may be able to distinguish between them from their position in the program. Avoid identifiers such as:
<a name="146"></a><a name="page56"></a> TYPE TRUE PROGRAM TASK RETURN STEP FUNCTION
The identifiers of IEC 1131-3 standard function blocks and functions as described in Appendix 1 should be regarded as reserved, such as:
TON RS SIN COS
[1]Keywords should be in upper case characters. However, an amendment to the 1993 standard for the second edition of IEC 1131-3 proposes that mixed case keywords should be allowed
