Using a Flexy 205 as a conduit between two devices

I use Flexys all the time, but I am trying to do something a little different this time and I’m wondering if it is as easy as it looks… or if it is deceptively difficult.

I normally set up a single IO Server connection to our Allen-Bradley PLC using ABLOGIX, and allow some tags to be read-only and some to be write-only. Now, we have a customer who wants us to talk to a third device using MODBUS via an RS-485 connection. The tricky part is that I need to have the AB PLC read several values that will be supplied by the MODBUS device.

How do I set up an eWON tag so that it is WRITTEN by the MODBUS device, but is read by the ABLOGIX device?

Hello @mitchell.hein,

If you want to use a flexy for this you would have the flexy read tags on the ABLOGIX PLC you could then publish the tags on the modbus side with the flexy acting as a modbus TCP server.

You might also be interesting in an Anybus X-gateway. The AB7632 is a modbus-TCP server and Ethernet/IP adapter. This allows a modbus TCP device to read and write data on one side which is exchanged with the EIP side so a plc, like an Allen Bradly, can read and write data. We have a range or other xgateways you can pick from. Select Anybus X-gateway


How do you publish the MODBUS tags to the ABLOGIX tags?
Do I have to use scripting or is there a different feature which can do that?

All tags can be published by configuring the tag visibility in Tag configuration.

You will also need to enable the Modbus TCP server. This can be found in the modbus IO server settings.

Sorry to be so dense, but I’m hoping for a step-by-step guide on this. You lost me.

We will have the Flexy reading values from COM1 of a FLA3301 set up as RS485 and communicating via MODBUS. So, I will need to configure a MODBUS IO Server and create a tag named “Gallons” and point it at the correct address to obtain this value. That seems pretty straightforward.

I then want to be able to read that value in my PLC which is set up with a different IO Server (ABLOGIX). Are you telling me that I don’t have to set up a second tag to do this? That I can just publish the “Gallons” tag to the ABLOGIX server?

I expected I would have to create a second tag defined for the ABLOGIX IO Server which points to my PLC tagname and then (somehow) move the data value from one tag into the other.

Please explain how Tag Visibility and Publishing works and the steps I would need to take to configure my Flexy to automatically transfer the MODBUS value (Gallons) to the ABLOGIX IO Server (or to a second tag in the ABLOGIX server).

Thanks for understanding! This whole feature is totally new to me.

This changes my answer. To further clarify is the other modbus device a master or slave?

If it is a slave, you have the correct idea you will need to setup tags on both IO servers for each. You will then need a script that copies the data from the Modbus tag to the ABlogix tag. Here is an example using a timer.

TSET 1,1
ONTIMER 1, "goto updatetags"

ABlogixTag@ = ModbusTag@

You can also do this with an ONCHANGE

ONCHANGE "ModbusTag", "ABlogixTag@ = ModbusTag@"

You might also want to look at the Anybus HMS-en2Sse-r linking device designed for a setup like this.


There we go… that was actually the answer I anticipated.
Thanks for validating that.

Our MODBUS device is indeed a slave and copying the tags via a timed script is exactly the approach that makes the most sense to me.


Glad I was able to help! have a great week!