Can a controller act like a brain over Modbus tcp/ip


Can a controller act like a brain over Modbus tcp/ip? By which I mean, if I understand correctly, using Modbus and a brain, I can read inputs and set outputs. Can I do the same with a controller, even if it’s not running any programs? A dumb controller, basically.

The reason I’m asking is because I’m working on a project where at the moment all I need is simple I/O control over ethernet. But I’m betting a week’s salary that we’re actually going to need a PAC. And this will be learned when I’m already on-site in a foreign country with two days left until turn-on.


Hello ShowNet!

Welcome to the OptoForums. I believe the short answer is “yes,” but let me expound on that to make sure we’re understanding each other correctly.

BTW, good job thinking ahead, especially given the foreign country, 2-days thing!

Our PACs all have native Modbus/tcp support (they act as Modbus slaves, straight out of the box), so you can use a Modbus client (I use Modscan32 for testing) to read/write. Super easy.

I’d say it’s a good idea to get a PAC-R (which is the [U][B]not-so-dumb brain[/B][/U] + controller) vs. just a PAC-EB (just the no-so-dumb brain w/no controller) if you have that option. Some people even buy PAC-Rs and shut of the “control engine” if that need a beefier brain.

If you want your PAC to act as a master, then that gets more complicated and would require a controller, but I don’t think that’s what you’re asking, right?

Also check out [B]this landing page on Modbus for more details[/B]/overview.

Safe travels!



This is an excellent answer, it’s exactly what I needed. Thank you!


You’re most welcome!

BTW, another reason to go for the PAC-R vs. -EB is if you want to quickly roll your own mobile app, since [I][U]groov[/U][/I] lets you quickly build an interface for your smartphone (or other device with a browser).

If you have the -R then you could build a little custom mobile interface for your I/O in like 5 minutes. Ben even made some [U][B]videos to prove it[/B][/U]. Did I mention there’s a [U][B][URL=“”]free trial[/B][/U]? Forgive the pitch, it’s just so fun I couldn’t resist mentioning that. Also, if you don’t need a custom interface, but could use a little app in your phone or testing out Opto-connected hardware, we do have a couple other apps that are great for commissioning. Check out this [B][U][URL=“”]tech note on all Opto 22 mobile apps[/U][/B].

What are you building? Can you share? We love hearing about OptoStuff in the wild! The SHOWnet must go on?