TcpListen

Description

This function block creates a new socket by performing the bind and listen operations using default TCP settings. You will have to use the TcpClose function block to release the socket returned by TcpListen.

Figure 8-222: The TcpListen function block

Related Functions

TcpAccept, TcpBinReceive, TcpBinSend, TcpClose, TcpConnect, TcpIsConnected, TcpIsValid, TcpReceive, TcpSend

Arguments

Input

Execute	Description	On the rising edgeA rising edge is the transition of a digital signal from low to high. It is also called positive edge listen for socket connections
	Data Type	BOOL
	Range	0, 1
	Unit	N/A
	Default	—
Port	Description	The network port to use
	Data Type	DINT
	Range	N/A
	Unit	N/A
	Default	—
Backlog	Description	The size of the queue for pending connections. If more than Backlog number of connection attempts are made prior to a TcpAccept call, then the controller may refuse the connections.
	Data Type	DINT
	Range	N/A
	Unit	N/A
	Default	—

Output

Done	Description	If TRUE, then the command completed successfully
	Data Type	BOOL
Error	Description	If TRUE, an error has occurred
	Data Type	BOOL
ErrorID	Description	Indicates the error if Error output is set to TRUE. See the table in Search IndexFile and TCP/IP Function Block ErrorID Output
	Data Type	DINT
ListenID	Description	The ID of the new listen socket
	Data Type	UDINT

Example

Structured Text

(* TcpListen example *)
CASE StepCounter OF
0:
   Inst_TcpListen(TRUE, 1234, 2);
   StepCounter := StepCounter + 1;
1:
   Inst_TcpListen(TRUE, 1234, 2);
   IF Inst_TcpListen.Done THEN
      MyListenID := Inst_TcpListen.ListenID;
      Inst_TcpListen(FALSE, 0, 0);
      StepCounter := StepCounter + 1;
   END_IF;
END_CASE;