Siemens SIMATIC S7 System Manual page 521

The UDP_RECV instruction also returns the IP address and port number of the remote
device. This allows your program to respond to the remote device with a UDP_SEND where
the remote IP address and port are required parameters.
Table 9- 20
Parameter
EN
ConnID
MaxLen
DataPtr
Done
Busy
Error
Status
Length
IPaddr1
...
IPaddr4
RemPort
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Parameters of the UDP_RECV instruction
Declaration Data type
IN BOOL
IN WORD
IN WORD
IN DWORD
OUT BOOL
OUT BOOL
OUT BOOL
OUT BYTE
OUT WORD
OUT BYTE
OUT WORD
9.4 Open user communication library
Description
Enable input
The CPU uses the Connection ID (ConnID) num-
ber for this receive operation (defined during the
connect process).
The MaxLen is the maximum number of bytes to
accept (for example, the size of the buffer at
DataPt (1 to 1024)).
The DataPtr is the pointer to where the receive
data should be stored. This is an S7-200 SMART
pointer to I, Q, M, or V memory (for example,
&VB100).
The instruction sets the Done output when the
receive operation is complete with no errors.
When the instruction sets the Done output, the
Length output is valid.
The instruction sets the Busy output while the
receive operation is in progress.
The instruction sets the Error output when the
receive operation is complete with an error. Refer
to "Open user communication library instruction
error codes" (Page 524) for further information.
The Status output shows the error code if the
instruction sets the Error output. Status is zero
(no error) if the instruction sets the Busy or Done
outputs.
The Length is the actual number of bytes re-
ceived. Only when the instruction sets the Done
or Error outputs is the Length valid. If the instruc-
tion sets the Done output, then the instruction
received the entire message. If the instruction
sets the Error output, the message was greater
than the buffer size (MaxLen) and has been trun-
cated.
These are the four IP address octets of the re-
mote device that sent the message. IPaddr1 is
the most significant byte and IPaddr4 is the least
significant byte of the IP address.
The RemPort is the port number of the remote
device that sent the message.
Libraries
521