Instruction list
Instruction List (IL) is one of the 5 languages supported by the IEC 61131-3 standard. It is designed for programmable logic controllers (PLCs). It is a low level language and resembles assembly. All of the languages share IEC61131 Common Elements. The variables and function call are defined by the common elements so different languages can be used in the same program.
Program control (control flow) is achieved by jump instructions and function calls (subroutines with optional parameters).
The file format has now been standardized to XML by PLCopen.
Example
LD Speed
GT 2000
JMPCN VOLTS_OK
LD Volts
VOLTS_OK LD 1
ST %Q75
Variations from IEC61131
Many vendors whilst incorporating the full IEC61131 requirements have additional vendor specific calls/function blocks to suit their hardware such as reading or writing to I/O. Siemens PLC instruction list language is known as "Statement List" or "STL" in English, and "Anweisungs-Liste" or "AWL" in German, Italian and Spanish. The user of a Simatic development package may choose between German and International mnemonics to represent instructions. For example, "A" for "AND" or "U" for "UND", "I" for "Input" or "E" for "Eingang".