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

Table 28 - Standard comparison functions
Graphical form
Usage examples
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ANY_ELEMENTARY --| *** |--- BOOL
: --| |
ANY_ELEMENTARY --| |
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(***) - Name or Symbol
A := GT(B,C,D) ;
or
A := (B>C) & (C>D) ;
No.
Name
a
Symbol
 b
Description
5
GT
>
Decreasing sequence:
OUT := (IN1>IN2) & (IN2>IN3) & ... & (INn-1 > INn)
6
GE
>=
Monotonic sequence:
OUT := (IN1>=IN2)&(IN2>=IN3)& ... & (INn-1 >= INn)
7
EQ
=
Equality:
OUT := (IN1=IN2) & (IN2=IN3) & ... & (INn-1 = INn)
8
LE
<=
Monotonic sequence:
OUT := (IN1<=IN2)&(IN2<=IN3)& ... & (INn-1 <= INn)
9
LT
<
Increasing sequence:
OUT := (IN110
NE
<>
Inequality (non-extensible)
OUT := (IN1 <> IN2)
NOTE 1
The notations IN1, IN2, ..., INn refer to the inputs in top-to-bottom order; OUT
refers to the output.
NOTE 2
All the symbols shown in this table are suitable for use as operators in textual
languages, as shown in tables 52 and 55.
NOTE 3
Usage examples and descriptions are given in the ST language defined in 3.3.
a
When the named representation of a function is supported, this shall be indicated by the suffix “n”
in the compliance statement. For example, “5n” represents the notation “GT”.
b
When the symbolic representation of a function is supported, this shall be indicated by the suffix
“s” in the compliance statement. For example, “5s” represents the notation “>“.
2.5.1.5.5 Character string functions
All the functions defined in 2.5.1.5.4 shall be applicable to character strings. For the purposes of
comparison of two strings of unequal length, the shorter string shall be considered to be extended on
the right to the length of the longer string by characters with the value zero. Comparison shall proceed
from left to right, based on the numeric value of the character codes in the character set defined in
2.1.1. For example, the character string 'Z' shall be greater than the character string 'AZ', and 'AZ'
shall be greater than 'ABC'.
The standard graphical representations, function names and descriptions of additional functions of
character strings shall be as shown in table 29. For the purpose of these operations, character
positions within the string shall be considered to be numbered 1,2,...,L, beginning with the
leftmost character position, where L is the length of the string.
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61131-3 
 IEC:2003(E)
– 63 –
It shall be an error if:
- the actual value of any input designated as ANY_INT in table 29 is less than zero;
- evaluation of the function results in an attempt to (1) access a non-existent character position in
a string, or (2) produce a string longer than the implementation-dependent maximum string
length.