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User Guide

Driver Installation​

The USB TO RS485 (C) uses the FT232RNL chip. Most systems will automatically recognize it as a virtual COM port. If no available COM port appears in Device Manager, or if the serial device shows a yellow exclamation mark, manually install the FTDI VCP driver.

Manual Installation on Windows​

  1. Method 1: Download Driver Genius from the Internet and let it automatically detect and install the driver.

  2. Method 2: Install the driver manually (the following uses Windows 7 as an example).

  3. Connect the device to the computer via USB. In Device Manager, if the COM port has a yellow exclamation mark, the driver is not installed.

    COM port with yellow exclamation mark

  4. Download the software package from the official wiki. Double-click the application and click Extract:

    Driver installation 1

  5. Click Next:

    Driver installation 1

  6. Check "I accept this agreement", then click Next:

    Driver installation 1

  7. Wait for the installation to complete, then click Finish:

    Driver installation 1
    Driver installation 1

  8. Now check Device Manager; the COM port should be available for normal use.

    Driver installation 1

RS485 Wiring​

Connect the USB TO RS485 (C) to the target RS485 device:

USB TO RS485 (C)Target RS485 Device
A+A / 485+
B-B / 485-
GNDGND (connect as needed)
Wiring Recommendations

For short distances and low-interference environments, only A+ and B- may be sufficient for communication. For long-distance, multi-node, or high-interference environments, it is recommended to connect GND as a reference ground and to use appropriate termination resistors based on the bus topology.

RS485 Communication Test​

You can interconnect two USB TO RS485 converters or connect to a target RS485 device for testing.

  1. Connect A+ to A+, B- to B-, and GND if necessary.
  2. On the computer, open a serial debug assistant such as SSCOM.
  3. Select the appropriate COM port and set the same baud rate, data bits, parity, and stop bits.
  4. Send test data and observe the TXD/RXD LEDs and the receive window.
  5. If communication fails, try swapping A+ / B-, lowering the baud rate, checking termination resistors, and inspecting cable shielding and grounding.
Driver installation 1

Modbus Device Communication​

The USB TO RS485 (C) is a physical-layer interface converter; it does not have a built-in Modbus master or slave protocol stack. When connecting to Modbus RTU devices, the Modbus protocol must be implemented on the PC, industrial computer, single-board computer, or host software, and then the module is used to send and receive RS485 data.

Typical test procedure:

  1. Connect A / B / GND to the Modbus RTU device.
  2. Confirm the slave address, baud rate, parity, data bits, and stop bits.
  3. Use Modbus Poll, a serial debug assistant, or a custom host program to send Modbus RTU commands.
  4. Refer to the slave device protocol manual to confirm register addresses, function codes, and data formats.

Precautions for Isolated Applications​

  • The isolated design reduces interference coupling between the host side and the field side, but does not replace proper field grounding, shielding, and lightning protection.
  • Twisted-pair cable is recommended for the RS485 bus. Shielded twisted-pair cable is recommended for long-distance wiring.
  • 120 Ω termination resistors can be installed at both ends of the bus depending on communication distance and speed. If short-distance communication is abnormal, try removing termination.
  • For multi-node communication, a daisy-chain topology is recommended; avoid long star-type branches. When wiring near interference sources such as high-voltage equipment, frequency converters, and motors, increase separation distance or adopt shielding, grounding, and lightning protection measures.