Monitoring SNAP PAC via Modbus RTU

I am currently working on a job. I am trying to monitor some data from a SNAP-PAC-S1. I was not involved in the setup.

I am told that the current configuration is that the system I am monitoring is controlled via a SNAP-PAC-R1. We are not allowed to use Ethernet communication, so a SNAP-PAC-S1 was also provided. I was told that the sole purpose of the -S1 in this application is to serve me the data points over Modbus RTU. However, I cannot get my controller (Niagara JACE 7) to communicate to the -S1.


I attached the Modbus configuration to both devices. I am not sure how to navigate the -S1. Is there another menu where I can match up the -S1 settings to my Niagara Modbus settings?

Firstly, welcome to the forums.

There is a bit going on here, and several missing pieces… is it possible for you to sketch out a system diagram and post a (cell phone) photo of it?
Im kind of lost about the whole having an R1, not using Ethernet, so having to use an S1.

I am guessing that the JACE is only serial and the R1 does not have any serial modules?
Is the JACE RS232 or 422/485? If its 232, then there is a serial port on the top of the R1 and you could use that and forget the S1… But there may be more to this than my high level guess.

A bigger picture would be really helpful.

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I attached a sketch. Not sure when I will be back on site to get a picture.

I misspoke about not using Ethernet. The situation is that the customer will only allow certain controllers to have direct connection to their network. The JACE controllers are on the customer network. This eliminates the use Modbus TCP/IP in my application.

  1. The -R1 is controlling the water treatment. To tell you the truth I have not really looked at it.
  2. The -R1 is also connected to an Ethernet switch in the panel only.
  3. The Ethernet switch is then wired to the -S1.
  4. The -S1 being connected to the customer’s system via RS-485. It is being used as the connection point to the water treatment system.

For now, if I could establish communication with the -S1, I could worry about the rest later.

Thank you for the welcome. And I appreciate the response.

Ok, thats really helpful, thanks a heap.

Are you able to put your laptop into that same switch as the S1?
If so, I am guessing that you will need to self assign your laptop an IP address for its network interface that is in the same subnet as the PAC S1 (and R1).

Is the ‘Stat’ light on the S1 flashing orange? If so, that means it is looking for an IP address.
Once you have your laptop on that network, you will be able to use PAC Manager to assign an IP address to the S1.
Once you have the laptop and the S1 talking via PAC Manager, you can start to look for the JACE using our Modbus toolkit.

I would have to go and look again. The Ethernet side of this is another contractor’s work and I would not be comfortable changing anything. I was hoping there was a quick way just to get the Modbus serial communicating. I know that the status light for the RS-485 port (on the S1) was off.

The only way to start configuring the S1 for serial modbus is to connect to its IP address.
To do that, you will need to have a laptop on the same network as it is.
Once you do that, open PAC Manager;

From there you can find out the IP address of the S1 and connect to it and start to set things up.