Integrating third party equipment using Modbus


I don’t know the best place to start, so…

I have a piece of equipment from a vendor (large blower from EBM) that has Modbus capability.

I have a SNAP-PAC-R1 controller on a 16 position rack and have a SNAP-SCM-485-422 module in one of the locations.

I have downloaded and started to play with the Modbus integration kit.

The blower requires Modbus RTU communication, 19200 baud rate, even parity, 1 stop bit, and 8 data bits.

As I said, I have tried playing with the Modbus integration kit settings but have been unable to get any useful information through the module.

What I am really looking for is some advice on where to start to learn what enough about Modbus to get started with this.

I know this is vague, but any help/pointers would be appreciated.




i’m writing this from the head, so it’s mabye a little off, but it’s a start

1.set the comm parameters of 485 module in pac manager - inspect - serial to mach the blower settings
2. open the opto modbus example strategy, set the comm port setting to tcp: (22500 is the number of port on the rack if you plug the 485 module on the first position and the device in the first channel)
3. open the watch window (there are predefined wth files for every type of data you want to read from device… in most cases you’ll use 1 and 3) and then try to read some registers from blower documentation

also read this article, it has some usefull info on implementing modbus.


Hi Russ,

I’d start with this tech note about using Opto 22 hardware + Modbus.

The whole integration kit you mentioned is a bit large, you might check out this smaller example to first get you going.

Hope that helps!


Russ the first hting you need to know is what registers the app is using, what of these registers you need, and how they are using it. The last part refers to whether the register platform is starting with 0 or 1. You will see this in the aformentioned docs.

Next you need to set up a comm handle in Pac and set up the parameters like orm mentioned.

A simple way to get started is don’t use the all encompasing example. Just stick one of the modbus commands in a script block such as a read command with a 1 second loop and then start playing with the paramters until you get the hang of it. Don’t forget to bring the subroutine command you are using into Pac Control before trying to use it. Use a read multiple registers command and have it write to a table and you will see if you have the parameters right becuase the values that make sense will either be in the right register or off by one.

Acutally, I have done numerous implementations but I am not quite up to speed without going back over the lastest implementation with the latest version of SDK. I did recently provide an implementation for Krohne Flow meters where it gets all the important info and a lot of the fairly usless troubleshooting data as well on an R1 with the 485 module.