IEC61131 Common Elements

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IEC 61131-3 is a standard in PLC computer programming languages. The five languages

to which this standard applies share common elements so different languages can be used in the same program.

Contents

[edit] Data Types

  • Bit Strings - groups of on/off values
  • INTEGER - whole numbers
    • SINT - signed short (1 byte)
    • INT - signed integer (2 byte)
    • DINT - double integer (4 byte)
    • LINT - long integer (8 byte)
    • U - Unsigned - add a U to the type to make it unsigned integer.
  • REAL - floating point IEC 559 (IEEE)
    • 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 - character strings surrounded by single quotes.
    Escaped characters are preceded by a dollar sign.
    ($$ $' $L $N $P $R $T $xx) => ($ quote linefeed newline page(FF) return tab hex_value)
    • 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, UNIT, USINT
      • ANY_BIT - LWORD, DWORD, WORD, BYTE, BOOL
      • ANY_STRING - STRING, WSTRING
      • ANY_DATE - DATE, TOD, DT

[edit] Variables

Variable attributes: RETAIN, CONSTANT, AT

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

[edit] Configuration

  • Resource - Like a CPU
  • Tasks - Can be multiple per CPU.
  • Programs - Can be executed once, on a timer, on an event.

[edit] Program Organization Units

  • 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

[edit] Configuration, Resources, Tasks

  • Configuration - processing resources, memory for IO, execution rates, number of tasks.