MB-GATEWAY and Modbus v2 - Multiple Slaves?

Out of curiosity, I’ve been testing an MB-GATEWAY to see if it would allow us to connect to serial Modbus devices using Ignition’s Modbus v2 Driver. Here is what I’ve discovered.

If I set the Modbus address of the PLC to 1, I can shoot straight through and pull data. Easy as pie. What I’m trying to figure out now is, being that the MB-GATEWAY uses RS-422/485 and can support up to 128 serial devices at a time, how do I go about addressing the individual devices on the serial side?

KEPServer allows you to add the Slave address to the end of the IP address (ex:, which tunnels through and see the additional slaves (I just tested this and confirms that it works.) Is there an option to do something like this in Ignition and I just overlooked it, or am I out of luck on that part. Thanks!


If you’re configuring tags in the Ignition gateway on the addresses page for the device, then each row you configure has an option where you can specify the unit id.

If you’re configuring them in SQLTags by hand or via import, then you can prefix the modbuss address with the unit id like this:


This would address holding register 1 on unit id/slave id/address 2.

1 is implicit, anything else needs to be explicitly prefixed.

OK, that makes sense. This apparently isn’t my week. That’s the SECOND completely obvious thing I’ve missed. :blush: Hopefully next week will be a little better. Thanks, Kevin.