The 810309 TCP to RTU Converter Assembly enables the user to use Atonometrics Modbus RTU devices, such as the RDE300i and Mars Soiling Sensor, with their Modbus TCP network. 

The converter requires three connections as shown below: 

ConnectionFunctionCable & Ordering
Power In10-30 VDCUse cable 830303-xxx. Order separately. Various length options.
TCP InEthernet connection to your Modbus TCP data acquisition deviceUse cable 830261-xxx. Order separately. Various length options.
Power / RTU OutPower and Modbus RTU from 810309 converter to Atonometrics sensor device, e.g. Mars or RDE300iCable 830284-002 included in 810309 kit. 2 meters long. M12 5-pin Male-Male. 

Mechanical Dimensions and Layout

The converter assembly enclosure dimensions are provided below in inches [millimeters]. 

The interior of the converter assembly houses a PUSR USR-TCP232-410s converter unit.


See the diagram below for wiring details. The wiring graphic can be found on the inside of the enclosure lid. You may open the enclosure lid during configuration to observe the graphic and verify converter device operability.

Hardware Configuration

  1. Attach the 830284-002 power and Modbus RTU cable from the “Power out” port of the TCP to RTU Converter Assembly (810309) to the “Main” port of the Atonometrics device as shown in the wiring diagram above
  2. Attach the 830261-xxx ethernet cable from TCP to RTU Converter Assembly (810309) to the client device as shown in the wiring diagram above 
  3. Wire the 830303-xxx power cable as shown in the wiring diagram above. Ensure the power supply is 12-30 VDC and the brown and black wires are wired correctly. NOTE: for long cables, use higher power supply voltage, e.g. 24 VDC, to mitigate voltage drops on the cable.
  4. Turn the power supply on and open the TCP to RTU Converter Assembly (810309). Confirm that the “Power” and “Works” LEDs on the USR-TCP232-410s device are both glowing

LEDs on USR-TCP232-410s when power is supplied to Converter Assembly (810309) 

Testing with Long Ethernet Cables

Please be aware that when using long Ethernet cables certain Ethernet devices -- especially laptop computers -- may not function properly due to inability to drive signal through the cables. Therefore, when testing this system, ensure that your network equipment is able to work properly with the selected cables, or add an intermediate network device if needed.

Software Configuration

The 810309 converter assembly uses the PUSR USR-TCP232-410s converter device. This device must be configured for TCP to RTU conversion according to your network requirements. Configuration must be performed by the user using software provided by PUSR. Please use the procedure below to configure this device. You may also follow the link to PUSR documentation in the References section below. 

  1. Download Software: [USR-M4] USR-TCP232-M4K3 Setup Software V2.3.3.97
  2. On your Windows desktop: Start Menu->Control Panel -> Network and Sharing Center -> Connections: Ethernet -> Properties-> Internet Protocol Version 4 (TCP/IPv4)

Control Panel Navigation

  1. The default IP address for USR-TCP232-410s is

  2. Set the static IP of the client to an address with the same network and subnet identifier as the converter device, but use a unique host identifier (e.g., 192.168.201), subnet mask to, and default gateway to

Example: Static IP Address Configuration


  1. Open the USR-TCP232-M4, E45 software

  2. Click on “Search Device” and double click on USR-TCP232-410s device that populates in search list

  3. Click on the RS485 tab 

  4. Edit the data format settings to match the settings stored on the Atonometrics device 

  5. Select “TCP Server” for work mode

  6. Choose a local port. The default is 23 for RS-232 and 26 for RS-485. Take note of the selected port number. 

  7. Ensure the port numbers are not the same for RS-232 and RS-485, or else RS-485 will not work

  8. Click the “Save COM2” button on the RS485 tab

USR-TCP232-M4, E45 Software Interface


Changing TCP to RTU Converter Assembly (810309) IP Address

To change IP address of the TCP to RTU Converter Assembly (810309), configure settings in lower left corner of USR-TCP232-M4, E45 and press “Base Save” (this will be necessary if communicating with device on different network than default)

The new IP address must contain the same network and subnet identifiers as client and unique host identifier (I.e. repeat steps to change static IP address of PC to same network and subnet as newly selected TCP to RTU Converter Assembly (810309) address)

*Verify subnet mask and default gateway match network configuration

Modbus Configuration

Set the baud rate and data format to the same settings as the Atonometrics device. Change the ModbusTCP dropdown from “None” to “ModbusTCP.” Then press “Save COM2.”

Testing with Modbus Poll

Atonometrics recommends testing the TCP to RTU Converter Assembly (810309) with a third party Modbus tool such as Modbus Poll to verify operatio. See the References section below for links to the Modbus Poll website. Please follow the instructions below to test the converter. 

  1. At the toolbar (top left) area of Modbus Poll UI, press connection->connect

Opening the Connect menu

  1. Set “Connection” to “Modbus TCP/IP”

  2. Enter the IP address of TCP to RTU Converter Assembly (810309) 

    1. Default =

  3. The Server Port must be same as “local port” selected in USR-TCP232-410s software settings

  4. Leave other settings as default

  5. Press “OK”

Modbus Poll Connection Setup

  1. At the toolbar (top left) area of Modbus Poll UI, press setup->read/write definition

Opening Modbus Poll Connection Setup

  1. Change Slave ID to correct slave ID of the Atonmetrics device and select desired range of registers and function code. Here we are testing the TCP to RS-485 converter with an RDE300i.

Modbus Poll Read/Write Definition

  1. Press “Ok’ and communication will be established with the Atonometrics device

  2. According to the “Register Tables” section of the RDE300i User Guide, these registers are 32-bit floats with most significant bytes first. Therefore, in Modbus Poll, select the cells with the data, and from the Display menu, select 32 Bit Float and Big-endian

Configuring Output Data Format in Modbus Poll 

  1. Here, we can see the value of module voltage, module current, output voltage, output current, and RTD temperature, respectively. If RDE300i is currently connected inline, all of these values should be changing. If it is connected to a standalone module, the output voltage and current should not change since there is no string. In an office setting, only the RTD temperature should be changing. 

Reading RDE300i Outputs


If the device is not working properly, confirm power is supplied to the device by checking the LEDs on the USR-TCP232-410s inside of the TCP to RTU Converter Assembly (810309). The “Power” and “Works” LEDs should be glowing, and the “RX” and “TX” lights should be flickering to show that data is being sent and received. Ensure all cables are correctly wired, and terminals are secure. Confirm the IP address settings on your Atonometrics device and the TCP to RS485 converter. Ensure Modbus settings are the same on the TCP to RS485 converter and the Atonometrics device. Confirm the Atonometrics Modbus settings with a direct connection using an Atonometrics Configuration Kit. Contact Atonometrics for support.

Check LEDs on device


1.      USR-TCP232-410s User Manual: https://www.pusr.com/download/M4/USR-TCP232-410S_User_Manual_V1.0.0.pdf

2.      Modbus Poll User Manual: https://www.modbustools.com/mbpoll-user-manual.html#_modbus_poll