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Structured Text (ST)

Structured Text (ST) is a high-level, block-structured language with a syntax resembling Pascal or C. It is the primary language supported by the ZPLC Web IDE.

Basic Syntax​

PROGRAM Main
    VAR
        Counter: INT := 0;
        Threshold: INT := 100;
        Output_LED: BOOL := FALSE;
    END_VAR

    Counter := Counter + 1;

    IF Counter >= Threshold THEN
        Output_LED := TRUE;
        Counter := 0;
    ELSE
        Output_LED := FALSE;
    END_IF;
END_PROGRAM

Data Types​

ZPLC supports standard IEC data types mapped to strict C types internally:

  • BOOL (Boolean)
  • SINT, INT, DINT, LINT (Signed integers)
  • USINT, UINT, UDINT, ULINT (Unsigned integers)
  • REAL, LREAL (Floating point)
  • TIME, DATE, TOD, DT (Time data types)

Control Structures​

  • IF ... THEN ... ELSIF ... ELSE ... END_IF
  • CASE ... OF ... ELSE ... END_CASE
  • FOR ... TO ... BY ... DO ... END_FOR
  • WHILE ... DO ... END_WHILE
  • REPEAT ... UNTIL ... END_REPEAT