tc-advanced-patterns

name	tc-advanced-patterns
description	Use this skill when implementing advanced TwinCAT 3 (ExST) features. It covers Properties (GET/SET), Methods, initialization lifecycles (FB_init, FB_reinit, FB_exit), State Machine patterns, pragmas (attributes, conditional compiling, regions, message output), and PlcTaskSystemInfo access.
disallowedTools	["edit","write","replace_string_in_file","multi_replace_string_in_file","create_file","grep_search","file_search","list_dir"]

TwinCAT Advanced Patterns (Cap. 10, 11, 12)

Pointers and References

VAR
    stConfig  : ST_MachineConfig;
    pConfig   : POINTER TO ST_MachineConfig;
    refConfig : REFERENCE TO ST_MachineConfig;
    nSize     : UDINT;
END_VAR

pConfig := ADR(stConfig);
IF pConfig <> 0 THEN
    pConfig^.nSpeed := 100;
END_IF;
nSize := SIZEOF(stConfig);

refConfig REF= stConfig;
refConfig.nSpeed := 100;

State Machine Pattern

FUNCTION_BLOCK FB_StateMachine
VAR
    eState : E_MachineState := E_MachineState.IDLE;
END_VAR

CASE eState OF
    E_MachineState.IDLE:
        IF bStartCmd THEN
            eState := E_MachineState.INIT;
        END_IF;

    E_MachineState.INIT:
        IF bInitDone THEN
            eState := E_MachineState.RUNNING;
        ELSIF bError THEN
            eState := E_MachineState.ERROR;
        END_IF;

    E_MachineState.RUNNING:
        IF bStopCmd THEN
            eState := E_MachineState.STOPPING;
        END_IF;

    E_MachineState.STOPPING:
        IF bStopped THEN
            eState := E_MachineState.IDLE;
        END_IF;

    E_MachineState.ERROR:
        IF bReset THEN
            eState := E_MachineState.IDLE;
        END_IF;
END_CASE;

Property (GET/SET) — TwinCAT 3 Extension

FUNCTION_BLOCK FB_Motor
VAR
    fSpeed : REAL;   (* backing field: Hungarian notation, no leading _ *)
END_VAR

PROPERTY Speed : REAL    (* Property name: PascalCase, no Hungarian prefix *)

(* GET accessor *)
Speed GET:
    Speed := fSpeed;

(* SET accessor *)
Speed SET:
    IF Speed >= 0.0 AND Speed <= 3000.0 THEN
        fSpeed := Speed;
    END_IF;

Interface Implementation — TwinCAT 3 Extension

INTERFACE I_Actuator
METHOD Start : BOOL
METHOD Stop  : BOOL
END_INTERFACE

FUNCTION_BLOCK FB_Valve IMPLEMENTS I_Actuator
VAR
    bOpen : BOOL;
END_VAR

METHOD Start : BOOL
    bOpen := TRUE;
    Start := TRUE;
END_METHOD

METHOD Stop : BOOL
    bOpen := FALSE;
    Stop := TRUE;
END_METHOD

Methods

FUNCTION_BLOCK FB_Buffer
VAR
    aData  : ARRAY [0..99] OF INT;
    nCount : INT := 0;
END_VAR

METHOD Add : BOOL
VAR_INPUT
    nValue : INT;
END_VAR
    IF nCount < 100 THEN
        aData[nCount] := nValue;
        nCount := nCount + 1;
        Add := TRUE;
    ELSE
        Add := FALSE;
    END_IF;
END_METHOD

METHOD Clear : BOOL
    MEMSET(ADR(aData), 0, SIZEOF(aData));
    nCount := 0;
    Clear := TRUE;
END_METHOD

Pragmas & Attributes

Message Pragmas

{text 'Part compiled'}
{info 'TODO: rename'}
{warning 'Deprecated usage'}
{error 'Not implemented'}      (* Stops compilation *)

Key Attribute Pragmas

Attribute	Effect
{attribute 'pack_mode' := '1'}	Control struct alignment (0=8byte, 1=1byte, 2=2byte, 4=4byte)
{attribute 'qualified_only'}	Force GVL_Name.VarName / E_Name.eValue syntax
{attribute 'strict'}	Strict type checking for enums
{attribute 'enable_dynamic_creation'}	Required for __NEW dynamic allocation
{attribute 'call_after_init'}	Method called after FB_init and external assignments
{attribute 'call_after_online_change_slot'}	Method called after Online Change slot processing
{attribute 'call_on_type_change'}	Method called when type changes during Online Change
{attribute 'no_copy'}	Skip variable during Online Change copy
{attribute 'no-exit'}	Suppress FB_exit call
{attribute 'noinit'}	Skip initialization
{attribute 'obsolete'}	Mark as deprecated (generates warning)
{attribute 'instance-path'}	Get instance path as STRING
{attribute 'hide'}	Hide from symbol information
{attribute 'TcRpcEnable'}	Enable RPC for methods
{attribute 'linkalways'}	Always link even if unused

Conditional Pragmas

{define VARIANT1}
{define VERSION '2.0'}

{IF defined(VARIANT1)}
    sMode : STRING := 'Variant1';
{ELSIF hasvalue(VERSION, '2.0')}
    sMode : STRING := 'V2';
{ELSE}
    sMode : STRING := 'Default';
{END_IF}

Operator	Usage
defined(<id>)	Check if define exists
defined(variable: <var>)	Check if variable declared (impl only)
defined(type: <type>)	Check if type exists (impl only)
defined(pou: <pou>)	Check if POU exists (impl only)
hasvalue(<id>, '<val>')	Check define value
hasattribute(pou: <p>, '<a>')	Check POU attribute (impl only)
hastype(variable: <v>, <t>)	Check variable type (impl only)

Region Pragma

{region "Motor Control"}
    fbMotor(bStart := bCmd);
    IF fbMotor.bFault THEN
        eState := E_State.ERROR;
    END_IF;
{endregion}

Warning Suppression

{warning disable C0195}
    (* code that would normally trigger warning C0195 *)
{warning restore C0195}

FB_init, FB_reinit and FB_exit (Cap. 11)

FB_init

Implicitly available. Called by TwinCAT when FB instance is initialized. Do not call manually.

METHOD FB_init : BOOL
VAR_INPUT
    bInitRetains : BOOL;  (* TRUE = retain vars initialized *)
    bInCopyCode  : BOOL;  (* TRUE = instance is in copy code (online change) *)
    nComNum      : INT;   (* Additional custom input *)
END_VAR

Parameter values by operating case:

Case	bInitRetains	bInCopyCode
First/New Download	TRUE	FALSE
Online Change	FALSE	TRUE
TwinCAT Restart	FALSE	FALSE

• No SUPER^.FB_init call allowed.
• Additional inputs set in instance declaration: fbDev : FB_Device(nComNum := 1);

FB_reinit

Called automatically after instance copy during Online Change (when declaration changes).

METHOD FB_reinit : BOOL
(* For derived FBs: must explicitly call SUPER^.FB_reinit() *)

FB_exit

Called automatically before instance removal.

METHOD FB_exit : BOOL
VAR_INPUT
    bInCopyCode : BOOL;  (* TRUE = online change; FALSE = download/shutdown *)
END_VAR
(* Use to: release __DELETE memory, close handles, etc. *)
(* For derived FBs: derived FB_exit executes first, then base. *)

Operating Cases — Call Sequence

Step	First Download	New Download	Online Change
1	FB_init	FB_exit	FB_exit
2	External init	FB_init	FB_init
3	call_after_init	External init	External init
4	—	call_after_init	call_after_init
5	—	—	Copy process
6	—	—	FB_reinit

• Online Change with only implementation changes: FB_exit/FB_init/FB_reinit are NOT called.
• POINTER/REFERENCE variables may become invalid after Online Change — use {attribute 'call_on_type_change'}.

Global Data Types (Cap. 12)

PlcAppSystemInfo — _AppInfo

Field	Type	Description
AdsPort	UINT	ADS port of PLC application
BootDataLoaded	BOOL	PERSISTENT variables loaded without error
OldBootData	BOOL	PERSISTENT variables invalid (backup loaded)
AppTimestamp	DT	Compile time of PLC application
OnlineChangeCnt	UDINT	Online changes since last download
ProjectName	STRING(63)	Project name

nPort   := _AppInfo.AdsPort;
bLoaded := _AppInfo.BootDataLoaded;

PlcTaskSystemInfo — _TaskInfo[]

nIdx := GETCURTASKINDEXEX();
IF nIdx > 0 THEN
    nCycleUs := _TaskInfo[nIdx].CycleTime / 10;  (* convert to µs *)
END_IF;

Field	Type	Description
CycleTime	UDINT	Set task cycle time (× 100 ns)
CycleCount	UDINT	Cycle counter
LastExecTime	UDINT	Last cycle execution time (× 100 ns)
FirstCycle	BOOL	TRUE during first PLC task cycle
CycleTimeExceeded	BOOL	TRUE if cycle time was exceeded

Action (TwinCAT 3 Extension)

Actions are reusable sub-routines bound to a parent POU (FB or program). They share the parent's local variable scope — no own VAR_INPUT/VAR_OUTPUT.

FUNCTION_BLOCK FB_Pump
VAR
    bRunning : BOOL;
    nFaultCode : DINT;
END_VAR

ACTION ResetFault
    nFaultCode := 0;
    bRunning   := FALSE;
END_ACTION

(* Body: *)
IF bResetCmd THEN
    ResetFault();   (* Local action call *)
END_IF;

• Use ACTION for code reuse without parameter overhead.
• Use METHOD when you need parameters or a return value.
• An action cannot be called from outside the owning POU.

Additional Attribute Pragmas

Attribute	Effect
{attribute 'monitoring' := 'variable'}	Force watch monitoring as plain variable
{attribute 'monitoring' := 'call'}	Watch via implicit getter call
{attribute 'init_on_onlchange'}	Re-initialize on online change
{attribute 'analysis' := '-33'}	Disable specific static analysis rule
{attribute 'global_init_slot' := 'N'}	Force init order across GVLs
{attribute 'C++_Compatible'}	Force C++-compatible struct layout
{attribute 'reflection'}	Enable runtime reflection metadata
{attribute 'symbol' := 'read write'}	Control ADS symbol exposure

call_after_init Example

FUNCTION_BLOCK FB_Module
VAR
    bConfigured : BOOL;
END_VAR

{attribute 'call_after_init'}
METHOD AfterInit
    bConfigured := TRUE;   (* Runs after FB_init AND after instance assignments *)
END_METHOD

Useful when initialization depends on values written in the instance declaration that aren't yet available inside FB_init itself.

References (Beckhoff InfoSys)

• Pragmas
• FB_init, FB_reinit, FB_exit
• Global Data Types — System