FB_ConnectionlessSocket

A UDP socket can be managed (opened/generated and closed) with the function block FB_ConnectionlessSocket. FB_ConnectionlessSocket simplifies the implementation of a UDP application by encapsulating the functionality of the two function blocks FB_SocketUdpCreate and FB_SocketClose already internally. The integrated debugging output of the socket status facilitates troubleshooting in the event of configuration or communication errors. In addition, a minimum UDP application only requires an instance of the function block SocketUdpSendTod and/or an instance of the function block FB_SocketUdpReceiveFrom.

In the first step a typical UDP application opens a connection-less UDP socket with the function block FB_ConnectionlessSocket. In the next step instances of FB_SocketUdpSendTo and/or FB_SocketUdpReceiveFrom can be used for exchanging data with another communication device. When a UDP socket is closed depends on the requirements of the application (e.g. in the event of a communication error).

Inputs

VAR_INPUT
    sSrvNetID    : T_AmsNetID := '';
    nMode        : DWORD := 0;
    sLocalHost   : T_Ipv4Addr := '';
    nLocalPort   : UDINT;
    bEnable      : BOOL;
    tReconnect   : TIME := T#45s;(*!!!*)
END_VAR

Name	Type	Description
sSrvNetID	T_AmsNetID	String containing the AMS network address of the TwinCAT TCP/IP Connection Server. For the local computer (default) an empty string may be specified.
nMode	DWORD	Parameter flags (modes). The permissible parameters are listed here and can be combined by ORing. CONNECT_MODE_ENABLEDBG: Activates logging of debug messages in the application log. In order to view the debug messages open the TwinCAT System Manager and activate log view.
sLocalHost	T_Ipv4Addr	IP address (Ipv4) in string form (e.g. '172.33.5.1') of the local network adapter. An empty string may be specified for the default network adapter.
nLocalPort	UDINT	IP port number (e.g. 200) on the local computer.
bEnable	BOOL	As long as this input is TRUE, attempts are made cyclically to open a UDP socket until a connection has been established. An open UDP socket can be closed again with FALSE.
tReconnect	TIME	Cycle time with which the function block tries to open the UDP socket.

	Setting the cycle time for the connection The tReconnect value should not be set too low, since timeout periods of > 30 s may occur in the event of a network interruption. If the value is too low, command execution would be interrupted prematurely, and ADS error code 1861 (timeout elapsed) would be returned instead of the Winsocket error WSAETIMEDOUT.

Outputs

VAR_OUTPUT
    bBusy   : BOOL;
    bError  : BOOL;
    nErrId  : UDINT;
    hSocket : T_HSOCKET;
    eState  : E_SocketConnectionlessState := eSOCKET_CLOSED;
END_VAR

Name	Type	Description
bBusy	BOOL	TRUE, as long as the function block is active.
bError	BOOL	Becomes TRUE if an error code occurs.
nErrID	UDINT	If an bError output is set, this parameter returns the TwinCAT TCP/IP Connection Server error number.
hSocket	T_HSOCKET	Connection handle to the newly opened UDP socket. If successful, this variable is transferred to the instances of the function blocks FB_SocketUdpSendTo and/or FB_SocketUdpReceiveFrom.
eState	E_SocketConnectionlessState	Returns the current connection status.

Requirements

Development environment	Target system type	PLC libraries to include (category group)
TwinCAT v3.1.0	PC, or CX (x86, X64, ARM)	Tc2_TcpIp (communication)