Twincat and Structured Text

Getting in a new programming language can be difficult somethimes.
I will try to get you an short overview, to get started.

Variables

Variables are containers for storing data values.

 
VAR
    // Internal logic variable (no hardware link)
    bState:     BOOL;  
    // Flexible input (auto-assigned by TwinCAT)
    bSensor     AT %I*: BOOL;  // e.g., connected to a sensor  
    // Flexible output (auto-assigned by TwinCAT)
    nSetValue   AT %Q*: UINT;  // e.g., drives an actuator  
    // Optional: Directly addressed example
    // bEmergencyStop AT %IX5.3: BOOL;  // Input bit 5.3
END_VAR

Attributes

Variables can have some custom attributes,
which can help to debug code in online mode.
There are many more in the twincat documentation.

 
VAR
    {attribute 'hide'} 
    bHide:     BOOL;   // will be hidden
    {attribute 'displaymode':='hex'} 
    nValue     AT %I*: UINT;    // displayed as hex value
    {attribute 'TcDisplayScale' := '0-10'}
    nSetValue   AT %Q*: UINT;   // 0-10  
END_VAR

Datatypes

Variables must have a specified data type.

Structs

A STRUCT is define a group of variables

 
TYPE MotorData :
STRUCT
    speed:          REAL;
    current:        REAL;
    isRunning:      BOOL;
END_STRUCT
END_TYPE

Operators

How operators look like

Logical Operators

Bitwise Operators

Comparison Operators

If Statement

IF statement is used to test a condition and to execute the subsequent instructions

 
VAR
    bExecute:           BOOL;
    bCondition:         BOOL;
END_VAR

    // Simple IF statement
    IF bExecute THEN
        // Code executes only if bExecute is TRUE
    END_IF

    // IF-ELSE structure
    IF bExecute THEN
        // Runs when bExecute is TRUE
    ELSE
        // Runs when bExecute is FALSE
    END_IF

    // IF-ELSIF-ELSE structure (multiple conditions)
    IF bExecute THEN
        // Executes if bExecute is TRUE
    ELSIF bCondition THEN
        // Executes if bCondition is TRUE (bExecute is FALSE)
    ELSE
        // Executes if neither bExecute nor bCondition is TRUE
    END_IF

Switch Statement

CASE instruction is used to group multiple conditional instructions

 
VAR
    nSwitch:            INT;
END_VAR

    CASE nSwitch OF
        0: 
            // Code block for case x
        1: 
            // Code block for case y
    ELSE
        // Default code block (when no cases match)
    END_CASE

Loops

For Loop

FOR loop is used to execute instructions with a specific number of retries

 
VAR
    nIndex:             INT;
    aData:              ARRAY [0..9] OF REAL:= [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0];
END_VAR

    // mimimal example
    FOR nIndex := 0 TO 9 DO // with step width FOR nIndex := 0 TO 9 BY 1 DO
        // Output the current value of nIndex
        ADSLOGSTR(ADSLOG_MSGTYPE_HINT, 'Log Message: %s',  LREAL_TO_FMTSTR( aData[nIndex], 2, TRUE ));
    END_FOR

Exit a for loop early and return to the program flow

 
FOR nCounter:= 0 TO 10 DO
    IF nCounter >= 5 THEN
        EXIT;
    END_IF
END_FOR

While Loop

WHILE loop is used to execute instructions repeatedly until the termination condition applies

 
VAR
    nIndex : INT := 0; // Initialize index
END_VAR

    WHILE nIndex < 5 DO
        ADSLOGSTR(ADSLOG_MSGTYPE_HINT, 'Log Message: %s', INT_TO_STRING(nIndex));
        nIndex := nIndex + 1; // Increment index
    END_WHILE

Exit a while loop

 
WHILE nIndex < 5 DO
    IF nIndex >= 1000 then
         EXIT;   
    END_IF
    nIndex := nIndex + 1; // Increment index
END_WHILE

More will follow in part 2