Sending UDP messages to a video player

[Pete.S.]

Worst case scenario, I will have the PLC's spit out ASCII over RS485. I'll use a Raspberry Pi to intercept the RS485 ASCII, convert it and spit it back out over the network as UDP that my BrightSign can understand. The code to do that on a RPi should be fairly trivial.

In that case you can use modbus tcp and and skip the serial stuff. Your PLC supports modbus tcp and so does the raspberry pi with some libraries (or you can program it yourself). Sending UDP packets from RPI is done with regular socket programming.

There are plenty of modbus tcp clients and servers for testing and you can use wireshark to sniff on the modbus tcp messages.

 

[Brandon_K]

A simple 232 to Ethernet adapter. Use a raw ASCII message.

In that case you can use modbus tcp and and skip the serial stuff. Your PLC supports modbus tcp and so does the raspberry pi with some libraries (or you can program it yourself). Sending UDP packets from RPI is done with regular socket programming.

There are plenty of modbus tcp clients and servers for testing and you can use wireshark to sniff on the modbus tcp messages.

This is fantastic. I never bothered to think that a RPi would have any Modbus libraries available (that said, I'm still a newbie when it comes to dealing with anything Modbus. This is my first time dealing with industrial PLC's and ladder logic at all, in fact).

I take it I would setup the RPi to be a Modbus client and have my PLC's point to it? I have 4 PLC's that ideally would point to a single RPi to have it issue UDP messages. At most, there would be a total of 50 static messages between the 4 PLC's that need sent out. Not much workload for a RPi3 (which I happened to have ordered two spares from on my last Adafruit order).

 

[Jeebs]

UDP, like TCP, is transport layer.
Modbus, Ethernet/IP, etc are application layer.

"Ethernet/IP" is a proprietary protocol that can be used on several transport layers, not to be mistaken with Ethernet or TCP/IP.

If you are going for the Pi as a Modbus client, there's no need to use strings on the PLC side. Simple ints can be used. For control and selecting the message to send through UDP. Message list stored on the Pi, which offers more flexibility imo.


There are other PLC's, like the Siemens Step 7 series, that can do raw socket comms on TCP/IP and UDP.
And there are PLC's like yours, which can do a select few predetermined protocols.