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Enhancing a ModBus RTU Network
What should I do to connect more than 32 devices with ModBus RTU in one comm network?

What should I do to connect more than 32 devices with ModBus RTU in one comm network?

There are several recommendations about that the limit to have a "healthy" ModBus RTU network the maximum number of devices is 32. Nowadays I've been discussing with colleagues talking about the use of amplifiers to go up to 64 devices in one daisy chain

I'll be interested in your comments.

thanks in advance.

By Patrick Lansdorf on 11 December, 2018 - 7:31 am

Hi there,

You can use modbus concentrators, such as the Anybus Communicator.
Also see: https://www.anybus.com/products/gateway-index/anybus-communicator/detail/anybus-communicator---modbus-rtu

Theoretically, you can add 32 Modbus RTU slaves to it, and it will appear as one slave to your Modbuis RTU master.

Hope that this helps.
Patrick

You should use an RS-485 repeater when connecting more than 32 devices to a Modbus RTU network, although this may not actually be necessary depending on the devices on your network.

The limit of 32 devices is not really a device limit, but a load limit on the RS-485 bus. This limit is defined as 32 Unit Loads. Many devices today load the network with only a fraction of a Unit Load, such as 1/4, 1/8, or 1/10 Unit Loads. With these devices on the network, you can connect up to 128, 256, or 320 devices, respectively.

You should contact the vendor of the Modbus devices that you're using and ask if the device is a full Unit Load or if it is a fraction of a Unit Load.