Iec 61131-3 Second edition 2003-01 Programmable controllers – Part 3: Programming languages

Table 2 - Identifier features
No.
Feature description
Examples
1
Upper case and numbers
IW215 IW215Z QX75 IDENT
2
Upper and lower case, numbers,
embedded underlines
All the above plus:
LIM_SW_5 LimSw5 abcd ab_Cd
3
Upper and lower case, numbers,
leading or embedded underlines
All the above plus: _MAIN _12V7
2.1.3 Keywords
Keywords
are unique combinations of characters utilized as individual syntactic elements as defined in
annex B. All keywords used in this standard are listed in annex C. Keywords shall not contain
imbedded spaces. The case of characters shall not be significant in keywords; for instance, the
keywords “FOR” and “for” are syntactically equivalent. The keywords listed in annex C shall not be
used for any other purpose, for example, variable names or extensions as defined in 1.5.1.
NOTE National standards organizations can publish tables of translations of the keywords given
in
annex C.
2.1.4 Use of white space
The user shall be allowed to insert one or more characters of “white space” anywhere in the text of
programmable controller programs except within keywords, literals, enumerated values, identifiers,
directly represented variables as described in subclause 2.4.1.1, or delimiter combinations (for
example, for comments as defined in 2.1.5). “White space” is defined as the SPACE character with
encoded value 32 decimal, as well as non-printing characters such as tab, newline, etc. for which no
encoding is given in IEC/ISO 10646-1.
2.1.5 Comments
User comments shall be delimited at the beginning and end by the special character combinations
“(*” and “*)”, respectively, as shown in table 3. Comments shall be permitted anywhere in the
program where spaces are allowed, except within character string literals as defined in 2.2.2.
Comments shall have no syntactic or semantic significance in any of the languages defined in this
standard.
The use of nested comments, for example, (* (* NESTED *) *), shall be treated as an error
according to the provisions of 1.5.1 d).
The maximum number of characters allowed in a comment is an implementation-dependent
parameter.
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61131-3 
 IEC:2003(E)
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