FB_SocketUdpCreate

The function block FB_SocketUdpCreate can be used to open a client/server socket for the User Datagram Protocol (UDP). If successful, a new socket is opened, and the associated socket handle is returned at the hSocket output. The handle is required by the function blocks FB_SocketUdpSendTo and FB_SocketUdpReceiveFrom, for example, in order to exchange data with a remote device. If a UDP socket is no longer required, it can be closed with the function block FB_SocketClose. The port address nLocalHost is internally reserved by the TCP/IP Connection Server for the UDP protocol (a "bind" is carried out). Several network adapters may exist in a PC. The input parameter sLocalHost determines the network adapter to be used. If the sLocalHost input variable is ignored (empty string), the TCP/IP Connection Server uses the default network adapter. This is usually the first network adapter from the list of the network adapters in the Control Panel.

Automatically created network connections If an empty string was specified for sLocalHost when FB_SocketUdpCreate was called and the PC was disconnected from the network, the system will open a new socket under the software loopback IP address: '127.0.0.1'.

Automatically created network connections with several network adapters If two or more network adapters are installed in the PC and an empty string was specified as sLocalHost, and the default network adapter was then disconnected from the network, the new socket will be opened under the IP address of the second network adapter.

Setting a network address In order to prevent the sockets from being opened under a different IP address, you can specify the sLocalHost address explicitly or check the returned address in the handle variable (hSocket), close the socket and re-open it.

Inputs

VAR_INPUT
    sSrvNetId  : T_AmsNetId := '';
    sLocalHost : T_IPv4Addr := '';
    nLocalPort : UDINT;
    bExecute   : BOOL;
    tTimeout   : TIME:= T#5s;
END_VAR

Outputs

VAR_OUTPUT
    bBusy     : BOOL;
    bError    : BOOL;
    nErrId    : UDINT;
    hSocket   : T_HSOCKET;
END_VAR