USB to RS485 Cable for Modbus RTU
The USB Dongle for Modbus RTU is a USB to RS485 cable that connects your PC to Modbus RTU devices through an RJ45 connector. With it, your PC works as a Modbus RTU Master or Modbus RTU Slave. Read registers, simulate devices and debug your Modbus application right from your desk.
Inside, an FTDI USB-to-UART converter drives an RS485 transceiver. Because FTDI chips are widely supported, the cable appears as a standard COM port and usually works without installing any drivers.
Applications
- Chip evaluation: test our IS4310 and IS4320 Modbus chips with their Kappa evaluation boards, without writing any PC software.
- Modbus Master: read and write the registers of sensors, PLCs, meters and drives from a Modbus RTU master program.
- Modbus Slave: simulate a slave device on your PC while you develop the master side of your own product.
- Test automation: write your own Modbus RTU test scripts, for example in Python.
How the USB to RS485 Cable Works
Your PC sees the cable as a standard serial (COM) port. When your software sends a Modbus RTU frame, the FTDI chip converts it from USB to UART. Then, the transceiver puts it on the RS485 bus, and the replies follow the same path back to your PC.
As a result, any software that can open a COM port can communicate over Modbus RTU. You set the baud rate, parity and stop bits in your software, so the cable adapts to each device.
Standard Modbus RTU RJ45 Pinout
The RJ45 connector follows the standard Modbus RTU pinout: pin 5 is A and pin 4 is B. Therefore, the cable plugs directly into any Modbus RTU device that uses the same pinout. This includes all INACKS Modbus RTU products with an RJ45 connector.
Important: although the connector is an RJ45 connector, this cable is not intended for Ethernet communications. It uses RS485, not Ethernet. Do not connect it to an Ethernet port, such as those found on routers, switches, PCs or other Ethernet equipment.
Hardware Features
- FTDI USB-to-UART converter: standard virtual COM port on Windows, Linux and macOS.
- RS485 transceiver: 2-wire RS485 interface (A and B) for Modbus RTU.
- Connectors: USB-A plug on one end and RJ45 plug on the other.
- Cable length: approximately 0.5 m.
- Non-isolated: designed for bench testing, development and short connections. For long cable runs or large ground potential differences, we recommend galvanic isolation.
Compatible INACKS Products
The cable works with all our Modbus RTU products that have an RS485 RJ45 connector, for example:
- Kappa4310Ard and Kappa4310Rasp: IS4310 Modbus RTU Slave evaluation boards. Your PC acts as the Modbus Master.
- Kappa4320Ard and Kappa4320Rasp: IS4320 Modbus RTU Master evaluation boards. Your PC acts as the Modbus Slave.
- IS4310-M3 and IS4310-ISO485M6: Modbus RTU Slave modules with RJ45 connectors.
Quick Start with the USB to RS485 Cable
- Connect the USB to RS485 cable to your PC. It appears as a new COM port on Windows, or as a /dev/ttyUSB device on Linux.
- Then, plug the RJ45 connector into your Modbus RTU device, for example a Kappa4310Ard.
- Open your Modbus software, select the COM port and use the same serial settings as your device. For example, the IS4310 uses 19200 bps, even parity and 1 stop bit by default.
- Finally, read or write registers. For example, use qModMaster to read the Holding Registers of the IS4310 at slave ID 1.
Do you prefer to write code? The cable works with any programming language that can open a serial port. In Python, for example, the minimalmodbus and pymodbus libraries implement Modbus RTU for you.
This company and the products provided herein are developed independently and are not affiliated with, endorsed by, or associated with any official protocol or standardization entity. All trademarks, names, and references to specific protocols remain the property of their respective owners.
(This product includes the USB to RS485 cable. Evaluation boards and other Modbus devices are not included.)
