Action

This statement reads the UDP header from the specified socket.

 

 

Syntax

UDPREADHEADER socket

 

 

Remarks

UDP packets start with a 8 byte header. This header contains the peer address, port and packet size. The UDPREADHEADER reads the header and places the information into the variables PEERADDRESS, PEERPORT and PEERSIZE.

 

After you have read the UDP header, you can use PEERSIZE to read the number of bytes available in the packet.

 

Socket is a constant or variable in the range from 0-3. And 0-7 for the W5200/W5300.

UDPREADHEADER is only available for the W5x00.

 

 

 

See also

UDPREAD, CONFIG TCPIP , TCPREADHEADER

 

 

Example

'-----------------------------------------------------------------------------------------
'name                     : udptest_SPI.bas
'copyright                : (c) 1995-2025, MCS Electronics
'purpose                  : start the easytcp.exe program after the chip is programmed and
'                           press UDP button
'micro                    : Mega88
'suited for demo          : no
'commercial addon needed  : yes
'-----------------------------------------------------------------------------------------
 
$regfile = "m88def.dat"                                     ' specify the used micro
 
$crystal = 8000000                                         ' used crystal frequency
$baud = 19200                                               ' use baud rate
$hwstack = 64                                               ' default use 32 for the hardware stack
$swstack = 64                                               ' default use 10 for the SW stack
$framesize = 50                                             ' default use 40 for the frame space
 
 
Config Spi = Hard , Interrupt = Off , Data Order = Msb , Master = Yes , Polarity = Low , Phase = 0 , Clockrate = 4 , Noss = 0
'Init the spi pins
Spiinit
 
Print "Init , set IP to 192.168.1.70"                       ' display a message
Enable Interrupts                                           ' before we use config tcpip , we need to enable the interrupts
Config Tcpip = Int1 , Mac = 12.128.12.34.56.78 , Ip = 192.168.1.70 , Submask = 255.255.255.0 , Gateway = 192.168.1.1 , Localport = 5000 , Tx = $55 , Rx = $55 , Chip = W5100 , Spi = 1
 
 
 
Dim Idx As Byte                                             ' socket number
Dim Result As Word                                         ' result
Dim S(255) As Byte
Dim Sstr As String * 255
Dim Temp As Byte , Temp2 As Byte                           ' temp bytes
 
Const Showresult = 1
 
Print "UDP demo"
 
Dim Ip As Long
Ip = Maketcp(192.168.1.3)                                   'assign IP num
 
'like with TCP, we need to get a socket first
'note that for UDP we specify sock_dgram
Idx = Getsocket(idx , Sock_dgram , 5000 , 0)                  ' get socket for UDP mode, specify port 5000
Print "Socket " ; Idx ; " " ; Idx
 
'UDP is a connection less protocol which means that you can not listen, connect or can get the status
'You can just use send and receive the same way as for TCP/IP.
'But since there is no connection protocol, you need to specify the destination IP address and port
'So compare to TCP/IP you send exactly the same, but with the addition of the IP and PORT
Do
  Temp = Inkey()                                                ' wait for terminal input
  If Temp = 27 Then                                              ' ESC pressed
     Sstr = "Hello"
     Result = Udpwritestr(ip, 5000, Idx, Sstr, 255)
  Elseif Temp = 32 Then                                          ' space
    Do
        Waitms 200
        Dim Tel As Long : Incr Tel
        Sstr = "0000000000111111111122222222223333333333 " + Str(tel)
        Result = Udpwritestr(ip , 5000 , Idx , Sstr , 255)
    Loop
  End If
  Result = Socketstat(idx, Sel_recv)                        ' get number of bytes waiting
  If Result > 0 Then
    Print "Bytes waiting : " ; Result
 
     Udpreadheader Idx                                        ' read the udp header
 
    #if Showresult
        Print
        Print Peersize; " "; Peeraddress; " "; Peerport        ' these are assigned when you use UDPREAD
        Print Ip2str(peeraddress)                         ' print IP in usual format
    #endif
 
 
    If Peersize > 0 Then                                 ' the actual number of bytes
        Print "read" ; Peersize
        Temp = Udpread(idx, S(1), Peersize)             ' read the result
 
      #if Showresult
          For Temp = 1 To Peersize
            Print S(temp); " " ;                         ' print result
          Next
      Print "done"
      #endif
      Result = Udpwrite(ip, Peerport, Idx, S(1), Peersize)        ' write the received data back
    End If
  End If
Loop
'the sample above waits for data and send the data back for that reason temp2 is subtracted with 8, the header size
 
 
End