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[1] by the IEC; the current (third) edition was published in February 2013.[2]

Part 3 of IEC 61131 deals with basic software architecture and programming languages of the control program within PLC. It defines three graphical and two textual programming language standards:

Data types

  • Elementary Data Type
    • Bit Strings – groups of on/off values
      • BOOL - 1 bit (0,1)
      • BYTE – 8 bit (1 byte)
      • WORD – 16 bit (2 byte)
      • DWORD – 32 bit (4 byte)
      • LWORD – 64 bit (8 byte)
    • 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 literals
Unit Description
d Day
h Hour
m Minute
s Second
ms Millisecond
us Microsecond
ns Nanosecond
    • Duration [4]
      • TIME – (implementer specific). Literals in the form of T#5m90s15ms
      • LTIME – (8 byte). Literals extend to nanoseconds in the form of T#5m90s15ms542us15ns
    • Date
      • 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"
STRING escape sequences
Escape sequence Produces
$$ $
$' '
$L linefeed
$N newline
$P page (form feed)
$R return
$T tab
$xx hex value
  • Generic Data Types – Only available for the input / output/ in-out variables of system-defined Program Organization Units (POUs, see below)
    • ANY
      • ANY_DERIVED
      • ANY_ELEMENTARY
        • ANY_MAGNITUDE
          • ANY_NUM
            • ANY_REAL: LREAL, REAL
            • ANY_INT
              • ANY_UNSIGNED: ULINT, UDINT, UINT, USINT
              • ANY_SIGNED: LINT, DINT, INT, SINT
          • ANY_DURATION: TIME, LTIME
        • ANY_BIT: LWORD, DWORD, WORD, BYTE, BOOL
        • ANY_CHARS
          • 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.

Variables

Variable attributes: RETAIN, CONSTANT, AT

  • Global
  • Direct (local)
  • I/O Mapping – Input, Output, I/O
  • External
  • Temporary

Configuration

  • 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)

  • Functions
    • Standard: ADD, SQRT, SIN, COS, GT, MIN, MAX, AND, OR, etc.
    • Custom
  • Function Blocks
    • Standard:
    • Custom – Libraries of functions can be supplied by a vendor or third party.
  • Programs

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

References

  1. ↑ Stevic, Tom (5 May 2017). "A very short history of PLC programming platforms". Control Design. Retrieved 11 September 2021.
  2. ↑ "IEC 61131-3:2013". International Electrotechnical Commission (IEC). Retrieved 11 September 2021.
  3. ↑ PLCopen: The third edition of IEC 61131-3
  4. ↑ "Time Duration Literals (IEC 61131-3)".
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