Modbus Slave ID Setup


Thread Starter


Hi all!

I am currently trying to setup multiple Modbus slave devices and I cannot discover the devices.

I am using a MGATE MB3170 as a Gateway and 4 meter as Slave Devices.

Reading the meter manual said devices are setup with 48 as default slave Id.

I have a RS485 going from the gateway to the first meter then to the 2nd and so on. A to A, B to B and Comm to Comm. Ending with 120 ohm resistor.

My question is: If I connect all those 4 devices they will share the same slave Id which is 48. Do I need to change the slave id in each meter in order to pull data out ? Or the devices are smart enough to change automatically ?

Do I need to turn off and on after RS485 cable installation ? Do I lose the meter data if I restart the meter ?

Thank you in advance.
Yes, you will have to change the slave node ID address so each node has a unique, individual node ID address.

Sometimes that is done with DIP/rotary switches or jumpers, other times it's done in firmware setup.

You might not have to power cycle the slave after cable installation, but many devices do not recognize changes to serial settings or slave node ID changes unless the device is power cycled (Power turned on or off). Sometimes the manual tells you that, other times it doesn't. As to other aspects of what the meter remembers or not after a power cycle, I have no idea.

Note that since all the slaves are the same brand and model, the driver wiring is A to A, B to B. The master might not use the same convention for labeling the driver lines. So if you can't get any comm response, try swapping the driver lines at the master, because sometimes the lines are labeled backwards of other vendors. Having drive lines backwards doesn't damage the drivers, but comm won't work.

Thank you David for your explanation!

This is the meter I am trying to setup:


Section F on page 53 describe the Modbus info.
I saw the register 256 Modbus unit id. I am not sure how to change this. I didn't find on this manual how the manufacturer recommends to change the slave Id.

Is there any other recommendation to know how I can find out how to change the slave ID on these devices?

Thank you so much!
After a lot of research on the web, I read about a software named Addresser that let me change their slave ID. But I didn't find where to download the software.

Once again thank you for your help.

Looks like you need software from the manufacturer:

"Addresser is a convenient software kit that includes Addresser software, as well as an optically isolated ULINX RS485 to USB converter. The Addresser is a READ/WRITE Program with drop-down menus for convenient user interface between your PC or laptop
and the Modbus Terminals of the Sage Prime. Contact Sage for ordering information and instructions."

Looks like you can download instructions and software from;

good luck
Thank you for the info.

Is it a common practice that the manufacturer does not provide the way to change the Slave ID?

Reading the document I will need to contact them to order the software, in other words I cannot change the slave Id if I don't order that software.

I keep trying to find if I can download the Addresser software for free.

Once again thank you all for all your help.


Is a software package for setup common? Not really.

There are other Modbus field instruments that use a firmware/Modbus-writeable slave ID address, but those I've dealt with use a single slave ID register where you can write an interger value to the default slave ID register address and change the slave ID address to some other value.

This Sage uses the slave ID register for both the slave ID and something they call the "format flag", where the format flag is not defined. Nor is the high/low order byte order defined (which is low order byte, slave ID or format flag?) That makes writing to register 256 pretty dicey, because for all anyone knows format flag might change the serial settings.

A standing problem with firmware writeable slave ID's is not knowing what a device's current slave ID is. New, out-of-the-box, one can assume the slave ID is the default address. But what happens when once it's put into service, or someone dinks with it? I always attach an embossed stainless tag with serial settings and slave ID in case the device has to be replaced or handled off the installed network.

Siemens offers a free Windows utility 'scanner' for their Modbus Coriolis meter that sequentially polls serial settings and slave IDs hunting for a hit. Because of the number of combinations it could take minutes or hours to discover settings that are not default settings. And there's no 'reset-to-factory defaults' function. There are security issues in allowing a device to be easily reset to factory defaults, but one is spoiled by consumer stuff like a wireless router.
Once again thank you David!

When I read the manual I saw what you mentioned about the 256 register, is share with that flag and no explanation about it how you can change it.

Let keep trying to find more info about this.

Thank you all !!


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