Receiving UDP broadcast on S7-400 CP443-1

superted

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Jun 2011
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I am troubleshooting the setup of UDP broadcast receiving on a CP443-1 CP card. The telegrams appear in WireShark with IP 192.168.1.255 Port 7551. As long as the hardware config and NetPro connections are set up accordingly, and regardless of user program, shouldn't the message counters in NCM S7 Diagnostics, Industrial Ethernet Statistics section be counting up?

At the moment it seems only one message comes through, when the communication partner is restarted. I'm guessing this is a special telegram, and it seems the normal telegrams are filtered out by the CP card.

Thoughts?
 
The UPD packets have the disadvantage that there is no guarantee that they always reach their destination and this usually happens more in slow networks and even more through WiFi.

In addition, if the packet is sent in broadcast mode as indicated by IP 192.168.1.255, then it is still more likely to be lost than if it is sent to a specific IP.
 
I have zero experience with UDP broadcasts.

Only advice I can give is to follow this FAQ from Siemens:
How do you send/receive data to/from multiple communication partners via the IE CP of an S7-300 or S7-400 station using the UDP protocol?

Jesper, that was a worthwhile read. I've not seen use of unspecified UDP connections before. Very interesting how it basically allows you an unlimited number of communication paths, while only occupying 1 connection on the CP.

Unfortunately though, it's still point to point, not the UDP broadcast I need.
 
So I confirmed my own theory when I switched the communication partner to regular unicast. The counters in S7 NCM increase, even if no connections are configured and no com FB's /FC's are called.

Now the thing is that the counters only increase when I'm sending unicast, but not for broadcast. The manuals say the CP card supports broadcast, but obviously something is stopping the messages. I can't find any settings for it.
 
I suggest you take another look in your manual. Perhaps its different for different CP cards. This is taken from a CP443 manual perhaps you have your culprit here.


NoBrodcast.PNG
 
I suggest you take another look in your manual. Perhaps its different for different CP cards. This is taken from a CP443 manual perhaps you have your culprit here.


View attachment 53413

Well spotted Bratt (y), and it's the same for my CP I see.. What an annoying limitation. I know for certain I would not overload the CP with these broadcast telegrams.
 

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