gwSendPacket (Function)

This function sends a packet of binary data over the RTCU Communication Hub. It will return the status of the send command. See below.

 
Please note that the return value from this function should always be checked. There are a number of reasons why this function could fail - too much traffic on the network for example. Therefore, always check the return value, and, based on that, have a strategy for resending a message etc.

When Large Packet Support (LPS) is enabled, packets with up to 4064 bytes can be sent.

(See function overview for more more information about LPS)

Use the gwPacketSize function to determine the maximum size of a packet that can be sent to a receiver.

Input:        

receiver : DINT

NODE ID of receiver node.

buffer : PTR

The address of the receive buffer.

length : INT (1..4064)

Length of data to send (max 4064 bytes).

Returns: INT

Note: 128 - 255 is reserved for user-defined return codes from gwReceivePacketDone.

Declaration:

FUNCTION gwSendPacket : INT;
VAR_INPUT
  receiver : DINT;
  buffer   : PTR;
  length   : INT;
END_VAR;

Example:

INCLUDE rtcu.inc
 
PROGRAM test;
VAR
  incoming : gwReceivePacket;
  Buf_in : ARRAY [1..4064] OF SINT;
  Buf_out : ARRAY [1..4064] OF SINT;
  size     : INT;
END_VAR;
 
// Turn on power to the GSM module
gsmPower(power := TRUE);
gprsOpen();
 
// Wait for rch connection
WHILE NOT gwConnected() DO
  Sleep(delay := 2000);
END_WHILE;
 
// Determine the maximum size to send
size := gwPacketSize(nodeid := 2000);
IF size = 0 THEN
  size := 480;
END_IF;
 
// Set address BEFORE the 'incoming' is called the first time!
incoming.buffer   := ADDR(Buf_in);
incoming.maxlength := size;
 
BEGIN
  ...
  // Check for incoming packets
  incoming();
  IF incoming.sender > 0 THEN
     // A packet is received
     ...
  END_IF;
  ...
  gwSendPacket(receiver := 2000, buffer := ADDR(Buf_out), length := size);
  ...
END;
END_PROGRAM;