TABLE OF CONTENTS To ensure that IEC programs can be readily ported to different systems, all textual information should use a restricted set of letters, digits and characters. The standard requires that only characters from standard ISO 646 "Basic code table" are used. In practice, this character set is fairly generous and uses characters that are in everyday use on a PC; there are no unusual symbols.
The standard provides alternatives where there are conflicts between pound sign and number or hash sign # . Where a national character set does not have a vertical bar character for character based graphics, an exclamation mark can be used.
The use of special national characters, such as , is not permitted but such letters could be included as a national extension to the standard.
Optionally lower case letters can be used but they are not significant in language elements; for example, Heater1 and HEATER1 are treated as identical. However lower case letters are still significant if used to define printable strings such as Load Job la . Upper and lower case letters can be used within comments.
| Note | Identifiers are case insensitive but language keywords are case sensitive and should always be in uppercase. |
