Dear people,

I would like to create a TCP server in my PLC program. The TCP server needs to communicate with an external device. I have been searching the internet and found that the libraries Syssocket or CAA NetBaseSrv are two possible solutions to create a TCP server. From what I have read, CAA NetBaseSrv is more user-friendly to implement than the Syssocket variant.

However, I am still struggling to actually implement this library. Foremost is my little knowledge about creating a TCP server and how to read/understand each function block, especially the outputs of some blocks and the types, e.g. server has an output CAA.Handle, but I cannot find the explanation of CAA.Handle. I tried to find a good document that can help me understand how to implement a TCP server, but I could not find it.

Thank you in advance,
George

Hi George,

I am no expert but recently tried and got it working using this example project:
https://forge.codesys.com/prj/codesys-example/nbs/home/Home/#example-for-tcp-server-tcp-client

BR,
Rinie

Thank you for your advice Rinie,

I have tried to follow this example but found one problem.When I disconnect with Hercules the system does not acknowledge the lost of its connection this could result in critical errors.

Because of this error I am trying to implement the Syssocket library. With this library I am having a problem which I could not solve.

I have the following code:

ip_adres : STRING :='0.0.0.0';
port : WORD := 5000;    
iStep : INT := 1;


// Socket information


Socket_handler : SysSocket_Interfaces.RTS_IEC_HANDLE; 
Socket_handler_result : SysSocket_Interfaces.RTS_IEC_RESULT;


Socket_adress : SysSocket_Interfaces.SOCKADDRESS;

Addres_Convert : SysSocket_Implementation.RTS_IEC_RESULT; 

// Bind information
Bind_handler : SysSocket_Interfaces.RTS_IEC_RESULT;

// Listener Information
Listener_handler : SysSocket_Interfaces.RTS_IEC_RESULT;




Addres_Convert := SysSocket_Implementation.SysSockInetAddr(szIPAddress:= ip_adres,pInAddr:= ADR(Socket_adress.sin_addr)); 
Socket_adress.sin_family:= SysSocket_Interfaces.SOCKET_AF_INET; 
Socket_adress.sin_port := SysSocket_Implementation.SysSockHtons(usHost:= port);

CASE iStep OF
    1: 
    // Create Socket
    Socket_handler :=SysSockCreate(
        iAddressFamily :=SysSocket_Interfaces.SOCKET_AF_INET,
        diType:=SysSocket_Interfaces.SOCKET_STREAM,
        diProtocol:=SysSocket_Interfaces.SOCKET_IPPROTO_TCP,
        pResult:=ADR(Socket_handler_result)); 
    IF Socket_handler = SysSocket_Interfaces.RTS_INVALID_HANDLE THEN
            iStep := 1;
        ELSE
            iStep := 2;
        END_IF

    2:
        Bind_handler := SysSocket_Implementation.SysSockBind(
                            hSocket:=Socket_handler,
                            pSockAddr :=ADR(Socket_adress),
                            diSockAddrSize:=SIZEOF(Socket_adress) );



    3: 
        Listener_handler := SysSocket_Implementation.SysSockListen(
                                hSocket :=Socket_handler,
                                diMaxConnections :=1); 



END_CASE

When I am trying to get this working, the SysSockBind function gives a value of 16#207 which means adress already in use. I find this weird because of the IP-adress of 0.0.0.0. I think I am converting the Ip-adress in the wrong way, but the code does not give a error arround this. So therefore I cannot find the solution to this problem. I hope someone could help me with this problem.

Thanks in advance
George

Hi George,

I do not know what the problem is with the syssocket implementation, but when i read the forums it seems the Net Base Services library is the recommended way to go.

There is another more extensive example here:
https://forge.codesys.com/prj/codesys-example/plc-chat-nbs/home/Home/

I have just tested this example and it works very well, also with closing and opening the connection from hercules...

good luck!