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What's a conventional way to set an address and baud-rate/parity on a Modbus device?

Is this supposed to be done using hardware switches or can be done through a software?

If done through a software, can this software be connected on the Modbus line or this has to be done through a separate diagnostics port?

Chetan Bhargava
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udushu
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2 Answers2

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There isn't a standard way for this and it's up to a vendor to decide what settings he wants to provide open to a user and how these settings will be changed by the user. Baud rate and parity are almost always fixed and you can not change them. Address is usually changed using hardware switches. I have seen devices (usually gateways) with web interface where you can change all these and many other settings via web browser, and touch screen devices with embedded Linux where you set these settings via setup screens and/or menus, but these are more expensive and not so common devices that fit less then 3% of the total number of all MODBUS devices.

avra
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  • The Modbus standard states "9600 bps and 19.2 Kbps are required and 19.2 is the required default", so _if_ the baud rate is fixed the device should be using 19.2k, but since supporting 9600 is required as well there might be a way to switch. _If_ the device is truly standard compatible... – Tobias Kienzler May 12 '20 at 11:46
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There is really no standard. It's a choice left to the device designer. I've worked on a few ModBus instruments, and they were all 19200 8N1, but they all were from the same brand.

On every one, setup of modbus parameters were done from the device service menu or from the ModBus itself after setting a configuration dip switch (without the switch on, registers for those parameters are readonly)

Axeman
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