UDP Communication using 840Dsl

I recently came across an application for 840Dsl which required communication over ethernet from the PLC. Upon adding in the Siemens standard blocks (FB63-FB67) I found some gaping holes in the documentation which I hope to rectify.

Connection

Whether you are using TCP or UDP you will need to set up a connection. You do this in Net Pro: Select the CPU of the 840Dsl, right-click and choose New Connection. You will have to choose an ID for the connection and possibly a communication partner (unless you choose UDP broadcast/multicast). This part is key, because all the standard communication FBs will need to know this connection ID.

TCON

The documentation is largely sufficient to sort out what you should do here, however, it doesn’t tell you anywhere that the local_device_id in UDT65 should be B#16#4 for the Sinumerik 840Dsl – this is pivotal. Also, you will need to setup the connection ID in both the UDT65 data as well as the ID input for the TCON call.

TUSEND

My biggest problem using TUSEND was that I was consistently getting an error 80C4. A couple of things I found: multicast doesn’t appear to work, even if you have setup your UDP connection as multicast you will need to specify a receiver’s address; despite configuring the connection on the company network I found all my packets were going out over the Profinet bus – I needed to set the receiver’s address within the subnet of the Profinet I/O system and I had to connect my receiver on that bus.

Summary

UDP communication with 840Dsl is possible but it doesn’t work the way you’d expect.

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