(Optional) Add a Modbus RTU Interface

Owned by Nina Cardillo
Last updated: 28-Mar-2024
3 min read

For SmartServer 4.1 and prior, see (Optional) Add a Modbus RTU Interface (Release 4.1 and Prior).

This section consists of the following:

Connecting the Modbus RTU Interface

You can connect either RS-485 interface on a SmartServer IoT Pro EX to a Modbus RTU channel. You can only enable the Modbus interface on one RS-485 interface. That includes the RS-485 interfaces on both the SmartServer and any attached IOX I/O Expander Modules. If you enable the Modbus RTU interface on an IOX module, you cannot enable it on the SmartServer RS-485 1 or 2 interfaces, or any other attached IOX module. The default is to use the SmartServer RS-485 1 interface.

To connect a SmartServer RS-485 interface to a Modbus RTU channel, connect the RT+ and RT- receive/transmit data terminals and the SC signal common terminal to your RS-485 network.  You can optionally connect the SC terminal to earth ground at only one device on the RS-485 network. 


If you are using your SmartServer IoT as the earth ground reference, connect the earth ground input on the power supply input to earth ground, and connect the earth ground terminal on the RS-485 connector to the SC terminal with a jumper wire.


The RS-485 channel requires line termination as defined by the RS-485 standard.  Line termination is not provided by the SmartServer IoT. 

Configuring the Modbus RTU Interface

The RS-485 Configuration is available with the SmartServer IoT Pro EX Edition. This page displays the settings for RS-485 port 1 and RS-485 port 2, including bus type, baud rate, parity, and stop bits. Status and progress information is also displayed. By default, the channels are configured to support Modbus RTU. 

Setting the Modbus RTU Configuration

To enable the Modbus driver, or to verify that it is enabled, and to set the Modbus RTU device configuration settings, follow these steps:

  1. Open the SmartServer Configuration page as described in Accessing the SmartServer IoT Configuration Page. The Network tab appears as the default SmartServer IoT Configuration page. Once the network settings are configured for the SmartServer system, then the System tab will appear as the default.


    SmartServer IoT Network tab


    SmartServer IoT System tab


    For SmartServer Pi, open the SmartServer Configuration page as described in Accessing the SmartServer Pi Configuration Page. The left-side Configuration tab that appears depends on your cache data. As needed, click the SmartServer IoT tab. The System tab (top) will appear as the default as shown below.


    SmartServer Pi System tab

  2. Click the Modbus tab. The Modbus driver is enabled by default for SmartServer IoT and disabled by default for SmartServer Pi.


    SmartServer IoT Modbus tab


    SmartServer Pi Modbus tab

  3. Set the Modbus driver Enabled  option as needed.

  4. Click Update to save your configuration.

  5. Click the RS-485 tab. 


    SmartServer IoT RS-485 tab


    SmartServer Pi RS-485 tab

  6. Select Modbus for the Bus Type for either RS-485 1 or RS-485 2. Modbus can only be configured on one RS-485 port (default is port 1, RS-485 1).

  7. Set the bit rate (labeled Baud Rate), parity, and stop bits that you use on your Modbus RTU channel. The bit rate, parity, and stop bits must be the same for all devices on the Modbus RTU channel.  The default settings are 19200 bps, no parity, and 2 stop bits.

  8. Click Update to save your configuration.