TABLE OF CONTENTS Identifiers are used for naming different elements within the IEC languages, for example for naming variables, new data types, function blocks and programs.
An identifier can be any string of letters, digits and underlines provided that:
The first character is not a digit;
There are not two or more underline characters together.
The standard provides options for supporting identifiers with lower case letters, and identifiers with a leading underline character. There can be no embedded spaces.
The following are acceptable identifiers when all options permitted by the standard are supported:
The following are illegal:
The standard states that at least the first six characters should be tested for uniqueness. The following two identifiers may therefore be regarded as identical on some systems:
A12345_XY A12345_GG
Consequently to avoid the possibility of ambiguous identifiers, when developing software that may be ported to different PLC systems, always ensure that the first six characters are unique.
