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User Guide

Driver Installation​

The USB TO RS485 (E) uses the FT232RNL chip. After the operating system recognizes the device, it will be used as a virtual serial port. If the system does not generate a serial device, install the FTDI Virtual COM Port (VCP) driver for your operating system.

Interface Notes

The images below show the FTDI driver installation interface on Windows. The interface may vary depending on the driver version or operating system version.

Windows Manual Installation​

  1. Connect the converter to your computer. If the serial device in Device Manager shows a yellow exclamation mark, the driver is not properly installed.

    FTDI device not properly installed in Device Manager

  2. Download the driver for your operating system from the FTDI VCP driver page. Run the Windows installer and extract the installation files as prompted.

    Extracting FTDI driver installation files

  3. Read the license agreement, accept the terms, and proceed with the installation.

    Accepting the FTDI driver license agreement

  4. After installation is complete, unplug and reconnect the converter. Confirm the COM port number under "Device Manager" > "Ports (COM & LPT)".

    FTDI COM port generated in Device Manager

On Linux and macOS, confirm the device name in the system serial device list.

RJ45 Socket Wiring​

The RJ45 socket uses T568B pinout, but carries RS485 signals and auxiliary power — not Ethernet data.

RJ45 pinout reference
PinT568B ColorSignal
1White/OrangeA (A+)
2OrangeB (B-)
3White/GreenNC
4Blue5 V
5White/Blue5 V
6GreenNC
7White/BrownGND
8BrownGND
Verify Pinout Before Connecting

Different devices may have different RJ45 RS485 pin assignments. A standard straight-through cable only ensures pin-to-pin continuity; it does not guarantee signal compatibility with the peer device. Always consult the peer device's manual before connecting. Do not connect to an Ethernet port. If the peer device does not use the power pins, leave pins 4 and 5 disconnected. When using the 5 V auxiliary power, the load current must not exceed 100 mA.

Connecting to RS485 Devices​

  1. Insert a T568B straight-through cable with an RJ45 male plug into the converter's RJ45 socket.
  2. At the other end of the cable, use an RJ45 adapter board or make a custom wiring harness according to the target device's interface definition.
  3. Connect A and B, and decide whether to connect GND based on your field grounding scheme.
  4. Verify the contact numbering and signal definitions at both ends of the cable before connecting the USB end.
USB TO RS485 (E)Target RS485 Device
AA / D+ / 485+
BB / D- / 485-
GNDGND, connect according to site grounding scheme

Different manufacturers may label RS485 A and B oppositely. If communication fails after correct wiring, verify polarity against the target device's manual.

Termination​

The E model has a fixed 120 Ω termination resistor onboard, which cannot be disabled via switch. Termination resistors should generally be placed only at the two ends of an RS485 main line. Therefore, place this converter at a bus endpoint — do not use it as a middle node.

RS485 Communication Test​

  1. Connect the target RS485 device following RJ45 Socket Wiring and confirm A, B, and GND definitions.
  2. Connect the converter to the host and confirm the virtual serial port in the system.
  3. Open a serial debug tool, select the corresponding COM port, and set the baud rate, data bits, parity, and stop bits to match the target device.
  4. Send test data and check the receive window.
  5. If communication fails, check A/B polarity, serial parameters, termination, reference ground, and cable connections in sequence.

The supported communication rate range is 300 bps to 512000 bps. The actual rate must match the target device's settings.

Serial Debug Tool Communication Test Interface

Modbus RTU Device Communication​

The USB TO RS485 (E) performs physical-layer conversion between USB and RS485. It does not include a built-in Modbus protocol stack. When connecting to Modbus RTU devices, the host software or master application must generate and parse Modbus frames.

  1. Confirm the slave address, baud rate, parity, data bits, and stop bits.
  2. Use a Modbus debugging tool or custom program to open the serial port corresponding to the converter.
  3. Set the function code, register address, and data format according to the slave device protocol manual.
  4. Send requests and check responses and serial error messages.

Wiring Notes​

  • RS485 buses should use twisted-pair cables; shielded twisted-pair cables are recommended for long-distance or high-interference environments.
  • For multi-node communication, use a bus topology and avoid long star branches.
  • Isolation circuits do not replace on-site grounding, shielding, or lightning protection designs.
  • When routing cables near high-voltage lines, variable-frequency drives, or motors, maintain appropriate spacing, shielding, and grounding per site specifications.