This article relies largely or entirely on a single source. (March 2017)
IEC 61131-3 is the third part (of 10) of the international standard IEC 61131 for programmable logic controllers. It was first published in December 1993 by the IEC; the current (third) edition was published in February 2013.
- Ladder diagram (LD), graphical
- Function block diagram (FBD), graphical
- Structured text (ST), textual
- Instruction list (IL), textual (deprecated in 3rd edition of the standard)
- Sequential function chart (SFC), has elements to organize programs for sequential and parallel control processing, graphical.
- Elementary Data Type
- Bit Strings – groups of on/off values
- INTEGER – whole numbers (Considering byte size 8 bits)
- SINT – signed short integer (1 byte)
- INT – signed integer (2 byte)
- DINT – signed double integer (4 byte)
- LINT – signed long integer (8 byte)
- USINT – Unsigned short integer (1 byte)
- UINT – Unsigned integer (2 byte)
- UDINT – Unsigned double integer (4 byte)
- ULINT – Unsigned long integer (8 byte)
- REAL – floating point IEC 60559 (same as IEEE 754-2008)
- REAL – (4 byte)
- LREAL – (8 byte)
- Duration 
- TIME – (implementer specific). Literals in the form of T#5m90s15ms
- LTIME – (8 byte). Literals extend to nanoseconds in the form of T#5m90s15ms542us15ns
- DATE – calendar date (implementer specific)
- LDATE – calendar date (8 byte, nanoseconds since 1970-01-01, restricted to multiple of one day)
- Time of day
- TIME_OF_DAY / TOD – clock time (implementer specific)
- LTIME_OF_DAY / LTOD – clock time (8 byte)
- Date and time of Day
- DATE_AND_TIME / DT – time and date (implementer specific)
- LDATE_AND_TIME / LDT – time and date (8 byte, nanoseconds since 1970-01-01)
- Character / Character string
- CHAR – Single-byte character (1 byte, limited to characters 0 to 255 of ISO/IEC 10646)
- WCHAR – Double-byte character (2 byte, limited to characters 0 to 65535 of ISO/IEC 10646)
- STRING – Variable-length single-byte character string. Literals specified with single quote, 'This is a STRING Literal'
- WSTRING – Variable-length double-byte character string. Literals specified with a double quote, "This is a WSTRING Literal"
- Duration 
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- Generic Data Types – Only available for the input / output/ in-out variables of system-defined Program Organization Units (POUs, see below)
- ANY_REAL: LREAL, REAL
- ANY_UNSIGNED: ULINT, UDINT, UINT, USINT
- ANY_SIGNED: LINT, DINT, INT, SINT
- ANY_DURATION: TIME, LTIME
- ANY_BIT: LWORD, DWORD, WORD, BYTE, BOOL
- ANY_STRING: STRING, WSTRING
- ANY_CHAR: CHAR, WCHAR
- ANY_DATE: DATE_AND_TIME (DT), DATE_AND_TIME(LDT), DATE, TIME_OF_DAY (TOD), LTIME_OF_DAY(LTOD)
- User-defined Data Types
- Enumerated data type
- Enumerated data type with named value
- Subrange data type – puts limits on value i.e., INT(4 .. 20) for current
- Array data type – multiple values stored in the same variable.
- Structured data type – composite of several variables and types.
- Directly derived data type – type derived from one of the above types to give new name and initial value as a type.
- References – a kind of strongly typed pointer. Arithmetic operation of the value of this type is prohibited.
Variable attributes: RETAIN, CONSTANT, AT
- Direct (local)
- I/O Mapping – Input, Output, I/O
- Resource – Like a CPU
- Tasks – Can be multiple per CPU.
- Programs – Can be executed once, on a timer, on an event.
Program organization unit (POU)
- Standard: ADD, SQRT, SIN, COS, GT, MIN, MAX, AND, OR, etc.
- Function Blocks
- Custom – Libraries of functions can be supplied by a vendor or third party.
Configuration, resources, tasks
- Configuration – processing resources, memory for IO, execution rates, number of tasks.
Object oriented programming (OOP)
- The 3rd revision of the standard describes how to implement OOP within the application programming
- Stevic, Tom (5 May 2017). "A very short history of PLC programming platforms". Control Design. Retrieved 11 September 2021.
- "IEC 61131-3:2013". International Electrotechnical Commission (IEC). Retrieved 11 September 2021.
- PLCopen: The third edition of IEC 61131-3
- "Time Duration Literals (IEC 61131-3)".
- IEC 61131-3:2013 Programmable controllers - Part 3: Programming languages
- CODESYS important implementation independent of device manufacturers, includes object oriented programming (OOP) as an option
- de:STEP 7 implementation for Siemens devices, only