IEC 61131-3

IEC 61131-3 is the third part (of 8) of the open international standard IEC 61131 for programmable logic controllers, and was first published in December 1993 by the IEC. The current (third) edition was published in February 2013.

Part 3 of IEC 61131 deals with programming languages and defines two graphical and two textual PLC programming language standards:

• Ladder diagram (LD), graphical
• Function block diagram (FBD), graphical
• Structured text (ST), textual
• Instruction list (IL), textual (deprecated in 3rd edition of the standard ^[1])
• Sequential function chart (SFC), has elements to organize programs for sequential and parallel control processing.
• Continuous Function Chart (CFC). This language is an extension to the IEC 61131-3 standard, which gives free positioning of graphic elements.

Data types

• Bit Strings - groups of on/off values
  • BIT - 1 bit
  • 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 (1 byte)
  • INT - signed integer (2 byte)
  • DINT - double integer (4 byte)
  • LINT - long integer (8 byte)
  • U - Unsigned - prefix a U to the type to make it an unsigned integer.
• REAL - floating point IEC 60559 (same as IEEE 754-2008)
  • REAL - (4 byte)
  • LREAL - (8 byte)
• TIME - duration for timers, processes.
• Date and Time of day:
  • DATE - calendar date
  • TIME_OF_DAY - clock time
  • DATE_AND_TIME: time and date

STRING escape sequences

Escape sequence	Produces
$$	$
$'	'
$L	linefeed
$N	newline
$P	page (form feed)
$R	return
$T	tab
$xx	hex value

• STRING - character strings surrounded by single quotes. Escaped characters are preceded by a dollar sign.
  • WSTRING - holds multi-byte strings.
• Arrays - multiple values stored in the same variable.
• Sub Ranges - puts limits on value i.e., (4-20) for current
• Derived - type derived from one of the above types.
  • TYPE - single type
  • STRUCT - composite of several variables and types.
• Generic - groups of the above types:
  • ANY
    • ANY_DERIVED
    • ANY_ELEMENTARY
    • ANY_MAGNITUDE
      • ANY_NUM - LREAL, REAL
      • ANY_INT - LINT, DINT, INT, SINT, ULINT, UDINT, UINT, USINT
    • ANY_BIT - LWORD, DWORD, WORD, BYTE, BOOL
    • ANY_STRING - STRING, WSTRING
    • ANY_DATE - DATE, TOD, DT

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.

References

1. PLCopen: The third edition of IEC 61131-3

External links

• PLCopen
• IEC 61131-3:2013 Programmable controllers - Part 3: Programming languages
• PLC Introduction