How do I detect and report loss of connection to an RS-485 device?

Ewon Support
#1

I have a Flexy 205 that acts as a gateway between a PLC (via Ethernet) and a Dispenser (via an RS485 port). From time to time, the dispenser is powered off and it (obviously) loses communication with the Flexy.

How can I program a script in the Flexy to report the status of that connection back to the PLC, with 0 being bad and 1 being good? It seems like the quality value in the Flexy keeps that information in a similar way, but I’m not sure how to acquire the value of quality for a port and assign that to a tag in the Flexy for a particular port. Thoughts?

#2

What is the protocol that the dispenser uses to communicate with the Flexy, modbus?

#3

Yes. Modbus, two topics (A and B). Both ports (topics) are powered up together and are either both active or both are inactive.

#4

In that case, you could use the Status tag:

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The tag almost lines up with what you are looking for (0=bad 1=good) with the exception that 2 is also bad. If having the 2 messes you up, you could create a new tag and write a script where 2 also equals 0.

#5

I will need to pass this status back to my PLC (EtherNet/IP) via a tag, so I assume that I’ll have to write a script to access this STATUS tag. I have the periodic routine to check for other comm faults. What does the syntax look like to accomplish this for the RS485 Port?

PLC_STATUS_TAG@ = ???

#6

You should be able to setup an ONCHANGE for the status tag then write that value to a tag you have setup on the PLC.

#7

That’s a good idea, but what is the address for the first port on a RS485 Serial Module? Where can I find out what the addresses are for all the different ports on a Flexy? Is there a list?

#8

Hi @mitchell.hein,

How are you talking to the rs485 device currently? Is it a modbus device? You should be able to look at the address used for other tags for the device.