Question about CIP Generic and UDP

[Omnicode]

Hello, I am using a 1756-EN2T and tryin to communicate with a device that accepts ASCII string over ehternet usin UDP.

Do packets sent using CIP Generic of socket type "2 - UDP" look like a normal UDP packet i would send from software on a PC?

CreateSocket and WriteSocket all execute without error but I get no response from my device.

 

[lfe]

If your device expects a string of ASCII characters it will not understand the CIP protocol.

UDP, like TCP, is only a transport layer, the chain of bytes that is sent and received is defined by the protocol used, and obviously both sides should use the same protocol.

This is independent of whether the UDP packet is sent from a PC or a PLC.

In your case you should probably compose and send the ASCII characters expected by the protocol of that device

 

[Omnicode]

If your device expects a string of ASCII characters it will not understand the CIP protocol.

UDP, like TCP, is only a transport layer, the chain of bytes that is sent and received is defined by the protocol used, and obviously both sides should use the same protocol.

This is independent of whether the UDP packet is sent from a PC or a PLC.

In your case you should probably compose and send the ASCII characters expected by the protocol of that device

Thank you. This is what I suspected. I now have to figure out how to send an ascii string to my device from the plc over Ethernet.

 

[AustralIan]

The CIP Generic is a CIP message between the logix processor and the EN2T module.


See for example the WriteSocket chapter of:
https://literature.rockwellautomation.com/idc/groups/literature/documents/at/enet-at002_-en-p.pdf


Does the resulting UDP packet look exactly the same as a regular UDP packet? yes.


You would need to open a socket with OpenConnection, in order to listen for a response via ReadSocket.


Looks like there's some sample applications on the knowledgebase, as lined to in the user manual.

 

[Omnicode]

The CIP Generic is a CIP message between the logix processor and the EN2T module.


See for example the WriteSocket chapter of:
https://literature.rockwellautomation.com/idc/groups/literature/documents/at/enet-at002_-en-p.pdf


Does the resulting UDP packet look exactly the same as a regular UDP packet? yes.


You would need to open a socket with OpenConnection, in order to listen for a response via ReadSocket.


Looks like there's some sample applications on the knowledgebase, as lined to in the user manual.

Thanks. I have that manual memorized by this point. Short of trying to intercept the packets comming from the EN2T and looking at them, Im at a loss to troubleshoot.

 

[AustralIan]

Intercept makes sense then, and use wireshark.

 

[Jim3846]

You can tell exactly what your sending on the EN2T by using the internet explorer interface. Just type in the IP of the EN2T and view the Diagnostics. I think there is a place where it shows what is being sent to your device.

 

[Omnicode]

Intercept makes sense then, and use wireshark.

Thanks for the input, all.

So I got online with my laptop with Wireshark and set it up to pose as the receiving device. UDP packets sent from test software on my work computer were received fine. I triggered MSG from plc and received none.

Turns out...in the week of programming the other aspects of the project, I had set my MSG tags up and configured them to use a different EN2T than the one facing outward.

I went and reconfigured my MSG tags with the new path and all works as planned now.

Thanks much!

 

[AustralIan]

Ha, brilliant! Wireshark solves everything. 4.5 Stars