Create a "Standard project" and select CODESYS Control Win V3 as the device.
Define the target system by means of the Network scan.

As of SP16:

Open the Library Manager and add the following libraries:
Net Base Services
SysTypes2 interfaces
SysTimeRtc
Util

Create a global variable list named gvlSetting and define the following variables:

Declaration

VAR_GLOBAL CONSTANT
	gc_wMaxTelegram	: INT := 15;
	gc_uiPort		: UINT := 50001;
END_VAR
VAR_GLOBAL
	gc_stIpAddr		: String(19) := '192.168.99.109';
END_VAR

Adapt the IP address and the port to your system.

Create a new POU named TcpServer and adapt it as follows:

Declaration

VAR CONSTANT
	c_wMaxTelegram	: INT := 15;
END_VAR
VAR
	ipAddress		: NBS.IPv4Address;
	fbTcpConnection	: NBS.TCP_Connection;
	fbTcpServer		: NBS.TCP_Server;
	fbTcpRead		: NBS.TCP_Read;
	fbTcpWrite		: NBS.TCP_Write;
	
	
	abyRx			: ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
	abyTx			: ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
	
	iIndex			: INT;
	xRead			: BOOL := TRUE;
	xWrite			: BOOL := TRUE;
	xAckTelegram	: BOOL;
	xBlockAck		: BOOL;
	udiRead			: DINT;
END_VAR

Implementation

IF fbTcpRead.xReady THEN
	IF (fbTcpRead.udiCount = (gvlSetting.gc_wMaxTelegram + 1)) THEN	
		IF ((abyRx[0] = 87) AND  (abyRx[1] = 68) AND (abyRx[2] = 58) AND (abyRx[3] = 32)) THEN // 'WD: ' = Watchdog-Telegram
			FOR iIndex := 0 TO c_wMaxTelegram DO
				abyTx[iIndex] := 0;	 
			END_FOR
			// 'ACK: ' = Acknowledge-Telegram
			abyTx[0] := 65;
			abyTx[1] := 67;
			abyTx[2] := 75;
			abyTx[3] := 58;
			abyTx[4] := 32;
			// Receive-Counter
			abyTx[5] := abyRx[4];
			abyTx[6] := abyRx[5];
			abyTx[7] := abyRx[6];
			abyTx[8] := abyRx[7]; 
			xWrite := TRUE;
		END_IF
		xWrite := TRUE;
	END_IF
ELSIF fbTcpRead.xError THEN
	xRead := FALSE;
END_IF


fbTcpWrite(xExecute := xWrite AND NOT xBlockAck, itfConnection := fbTcpConnection, udiSize := SIZEOF(abyTx), pData := ADR(abyTx),  udiTimeOut := 0);
IF fbTcpWrite.xDone OR fbTcpWrite.xError THEN
	xWrite := FALSE;
END_IF

Create a new POU named TcpClient and adapt it as follows:

Declaration

VAR CONSTANT
	c_tInterval		: TIME := T#1S;
	c_udiInterval	: UDINT := 3 * TIME_TO_UDINT(c_tInterval)/1000;
END_VAR
VAR
	ipAddress		: NBS.IPv4Address;
	fbTcpClient		: NBS.TCP_Client;
	fbTcpRead		: NBS.TCP_Read;
	fbTcpWrite		: NBS.TCP_Write;
	
	abyTx			: ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
	abyRx			: ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
	
	fbBlink			: BLINK := (TIMELOW := c_tInterval, TIMEHIGH := c_tInterval);		
	xBlink			: BOOL; // Memory of the last state of PLC_PRG.fbBlink
	
	udiVal			: UDINT;
	pudiVal			: POINTER TO BYTE;
	iIndex			: INT;
	xConnect		: BOOL;
	
	xRead			: BOOL;
	xMissingAck		: BOOL;
	udiResult 		: UDINT;
	udiLastAck		: UDINT;
	udiNow			: UDINT;
	udiRead			: UDINT;
	eRErrorID 		: NBS.ERROR;
	eWErrorID 		: NBS.ERROR;
END_VAR

Implementation

IF NOT fbTcpClient.xActive THEN
	ipAddress.SetInitialValue(ipAddress := gvlSetting.gc_stIpAddr);
END_IF
fbTcpClient(xEnable := xConnect, itfIPAddress := ipAddress, uiPort := gvlSetting.gc_uiPort, udiTimeOut := 0);

fbBlink(ENABLE := TRUE);
IF (fbBlink.OUT AND (xBlink <> fbBlink.OUT) ) THEN
	udiVal := udiVal + 1;
	FOR iIndex := 0 TO gvlSetting.gc_wMaxTelegram DO
		abyTx[iIndex] := 0;
	END_FOR
	// 'WD: ' = Watchdog-Telegram
	abyTx[0] := 87;
	abyTx[1] := 68;
	abyTx[2] := 58;
	abyTx[3] := 32;
	// Counter
	pudiVal := ADR(udiVal);
	abyTx[4] := pudiVal^;
	pudiVal := pudiVal + 1;
	abyTx[5] := pudiVal^;
	pudiVal := pudiVal + 1;
	abyTx[6] := pudiVal^;
	pudiVal := pudiVal + 1;
	abyTx[7] := pudiVal^;
	fbTcpWrite(xExecute := xConnect,itfConnection := fbTcpClient.itfConnection, udiTimeOut := 0, udiSize := SIZEOF(abyTx), pData := ADR(abyTx));
ELSE
	fbTcpWrite(xExecute := FALSE);
END_IF

xBlink := fbBlink.OUT;

fbTcpRead(xEnable := xRead AND xConnect, itfConnection := fbTcpClient.itfConnection, udiSize := SIZEOF(abyRx), pData := ADR(abyRx), udiCount => udiRead);

IF fbTcpRead.xReady THEN
	IF (fbTcpRead.udiCount = (gvlSetting.gc_wMaxTelegram + 1)) THEN
		IF ((abyRx[0] = 65) AND  (abyRx[1] = 67) AND (abyRx[2] = 75) AND (abyRx[3] = 58) AND (abyRx[4] = 32)) THEN // 'WD: ' = Watchdog-Telegram
			udiLastAck := SysTimeRtc.SysTimeRtcGet(udiResult);
		END_IF
	END_IF
ELSIF fbTcpRead.xError THEN
	fbTcpRead(xEnable := FALSE);
END_IF


IF NOT fbTcpClient.xActive AND NOT fbTcpClient.xBusy AND NOT fbTcpClient.xDone THEN
	xConnect := TRUE;
ELSIF fbTcpClient.xDone THEN
	xConnect := FALSE;
END_IF

udiNow := SysTimeRtc.SysTimeRtcGet(udiResult);

IF (udiNow > (udiLastAck + c_udiInterval)) THEN  
	xMissingAck := TRUE;
ELSE
	xMissingAck := FALSE;
END_IF

Adapt the POU PLC_PRG as follows:
Implementation
TcpServer(); TcpClient();
Load the project to the controller and start it. Set The variable TcpClient.xRead to TRUE.

Up to SP16:

Open the Library Manager and add the following libraries:
CAA Net Base Services
SysTypes2 interfaces
SysTimeRtc
Util

Create a global variable named gvlSetting.

Adapt gvlSetting as follows:

Declaration

{attribute 'qualified_only'}
VAR_GLOBAL CONSTANT
    gc_uiPort        : UINT := 50001;
    gc_stIpAddr      : NBS.IP_ADDR := (sAddr := '192.168.99.74');
    
    gc_wMaxTelegram  : INT := 15; // Length o the telegram
END_VAR

Adapt the IP address and the port to your system.

Create a new POU named TcpServer and adapt it as follows:

Declaration

VAR CONSTANT
    c_wMaxTelegram  : INT := 15;
END_VAR
VAR
    fbTcpConnection : NBS.TCP_Connection;
    fbTcpServer     : NBS.TCP_Server;
    fbTcpRead       : NBS.TCP_Read;
    fbTcpWrite      : NBS.TCP_Write;

    abyRx           : ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
    abyTx           : ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;

    iIndex          : INT;
    xRead           : BOOL := TRUE;
    xWrite          : BOOL := TRUE;
    xAckTelegram    : BOOL;
    xBlockAck       : BOOL;
    udiRead         : UDINT;
END_VAR

Implementation

fbTcpServer(xEnable := TRUE, ipAddr := gvlSetting.gc_stIpAddr, uiPort := gvlSetting.gc_uiPort);
fbTcpConnection(xEnable := fbTcpServer.xBusy, hServer := fbTcpServer.hServer);

fbTcpRead(xEnable := fbTcpConnection.xActive, hConnection := fbTcpConnection.hConnection, szSize := SIZEOF(abyRx), pData := ADR(abyRx), szCount => udiRead);    

IF fbTcpRead.xReady THEN
    IF (fbTcpRead.szCount = (gvlSetting.gc_wMaxTelegram + 1)) THEN    
        IF ((abyRx[0] = 87) AND  (abyRx[1] = 68) AND (abyRx[2] = 58) AND (abyRx[3] = 32)) THEN // 'WD: ' = Watchdog-Telegram
            FOR iIndex := 0 TO c_wMaxTelegram DO
                abyTx[iIndex] := 0;     
            END_FOR
            // 'ACK: ' = Acknowledge-Telegram
            abyTx[0] := 65;
            abyTx[1] := 67;
            abyTx[2] := 75;
            abyTx[3] := 58;
            abyTx[4] := 32;
            // Receive-Counter
            abyTx[5] := abyRx[4];
            abyTx[6] := abyRx[5];
            abyTx[7] := abyRx[6];
            abyTx[8] := abyRx[7]; 
            xWrite := TRUE;
        END_IF
        xWrite := TRUE;
    END_IF
ELSIF fbTcpRead.xError THEN
    xRead := FALSE;
END_IF

fbTcpWrite(xExecute := xWrite AND NOT xBlockAck, hConnection := fbTcpConnection.hConnection, szSize := SIZEOF(abyTx), pData := ADR(abyTx),  udiTimeOut := 0);
IF fbTcpWrite.xDone OR fbTcpWrite.xError THEN
    xWrite := FALSE;
END_IF

Create a new POU named TcpClient and adapt it as follows:

Declaration

VAR CONSTANT
    c_tInterval   : TIME := T#1S;
    c_udiInterval : UDINT := 3 * TIME_TO_UDINT(c_tInterval)/1000;
END_VAR
VAR
    fbTcpClient   : NBS.TCP_Client;
    fbTcpRead     : NBS.TCP_Read;
    fbTcpWrite    : NBS.TCP_Write;

    abyTx         : ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;
    abyRx         : ARRAY [0..gvlSetting.gc_wMaxTelegram] OF BYTE;

    fbBlink       : BLINK := (TIMELOW := c_tInterval, TIMEHIGH := c_tInterval);        
    xBlink        : BOOL; // Memory of the last state of PLC_PRG.fbBlink

    udiVal        : UDINT;
    pudiVal       : POINTER TO BYTE;
    iIndex        : INT;
    xConnect      : BOOL;

    xRead         : BOOL := TRUE;
    xMissingAck   : BOOL;
    udiResult     : UDINT;
    udiLastAck    : UDINT;
    udiNow        : UDINT;
    udiRead       : UDINT;
END_VAR

Implementation

fbTcpClient(xEnable := xConnect, ipAddr := gvlSetting.gc_stIpAddr, uiPort := gvlSetting.gc_uiPort, udiTimeOut := 0);

fbBlink(ENABLE := TRUE);
IF (fbBlink.OUT AND (xBlink <> fbBlink.OUT) ) THEN
    udiVal := udiVal + 1;
    FOR iIndex := 0 TO gvlSetting.gc_wMaxTelegram DO
        abyTx[iIndex] := 0;
    END_FOR
    // 'WD: ' = Watchdog-Telegram
    abyTx[0] := 87;
    abyTx[1] := 68;
    abyTx[2] := 58;
    abyTx[3] := 32;
    // Counter
    pudiVal := ADR(udiVal);
    abyTx[4] := pudiVal^;
    pudiVal := pudiVal + 1;
    abyTx[5] := pudiVal^;
    pudiVal := pudiVal + 1;
    abyTx[6] := pudiVal^;
    pudiVal := pudiVal + 1;
    abyTx[7] := pudiVal^;
    fbTcpWrite(xExecute := xConnect,hConnection := fbTcpClient.hConnection, udiTimeOut := 0, szSize := SIZEOF(abyTx), pData := ADR(abyTx));
ELSE
    fbTcpWrite(xExecute := FALSE);
END_IF

xBlink := fbBlink.OUT;

fbTcpRead(xEnable := xRead AND xConnect, hConnection := fbTcpClient.hConnection, szSize := SIZEOF(abyRx), pData := ADR(abyRx), szCount => udiRead);

IF fbTcpRead.xReady THEN
    IF (fbTcpRead.szCount = (gvlSetting.gc_wMaxTelegram + 1)) THEN
        IF ((abyRx[0] = 65) AND  (abyRx[1] = 67) AND (abyRx[2] = 75) AND (abyRx[3] = 58) AND (abyRx[4] = 32)) THEN // 'WD: ' = Watchdog-Telegram
            udiLastAck := SysTimeRtc.SysTimeRtcGet(udiResult);
        END_IF
    END_IF
ELSIF fbTcpRead.xError THEN
    fbTcpRead(xEnable := FALSE);
END_IF

IF NOT fbTcpClient.xActive AND NOT fbTcpClient.xBusy AND NOT fbTcpClient.xDone THEN
    xConnect := TRUE;
ELSIF fbTcpClient.xDone THEN
    xConnect := FALSE;
END_IF

udiNow := SysTimeRtc.SysTimeRtcGet(udiResult);

IF (udiNow > (udiLastAck + c_udiInterval)) THEN  
    xMissingAck := TRUE;
ELSE
    xMissingAck := FALSE;
END_IF

Adapt the POU PLC_PRG as follows:
Implementation
TcpServer(); TcpClient();

Load the project to the controller and start it.