USB TO RS485 (C) User Guide

Features

USB‑to‑RS485 communication with hardware‑automatic data direction control
FT232RNL chip for good compatibility, stable, and reliable communication
Onboard isolated transceiver integrating electrical isolation and ESD protection
RS485 interface with surge, lightning, and ESD protection
Onboard resettable fuse and protection diodes for enhanced overcurrent, overvoltage, and transient protection
Onboard PWR, TXD, RXD LEDs for easy monitoring of power and data status
Supports Windows, Linux, Mac, Android, WinCE, and other operating systems

Specifications

Parameter	Description
Product Type	Industrial‑grade isolated USB to RS485 converter
Host Interface	USB
Device Interface	RS485
USB Connector Type	USB-A
USB Operating Voltage	5 V
Communication Chip	FT232RNL
Data Rate	300 bps ~ 512000 bps
RS485 Pins	A+, B‑, GND
RS485 Connector Type	Screw terminal
Direction Control	Hardware automatically controls data direction
RS485 Nodes	Point‑to‑multipoint, up to 32 nodes; more than 16 nodes recommend using a repeater
RS485 Transmission Distance	Approximately 1200 m at low baud rates
USB Transmission Distance	Approximately 5 m
RS485 Termination	Onboard 120 Ω balancing resistor
Interface Protection	600 W surge/lightning protection, 15 kV ESD protection
Isolation Method	Optical isolation
Isolation Voltage	Up to 2.5 kV
Operating Temperature	-40℃ ~ 85℃
Operating Humidity	5%RH ~ 95%RH
Supported Operating Systems	Windows 11 / 10 / 8.1 / 8 / 7 / XP, Mac, Linux, Android, WinCE

LED Indicator Descriptions

LED Indicator	Status Description
PWR	Power indicator, lights when USB is connected and voltage is detected
TXD	Transmit indicator, lights when data is being sent from the USB port
RXD	Receive indicator, lights when data is returned from the RS485 device side

Interface Description

Interface	Description
USB‑A	Connects to host devices such as PC, industrial computer, Raspberry Pi, Jetson
A+	RS485 differential signal A
B‑	RS485 differential signal B
GND	RS485 side reference ground; recommended for long‑distance or multi‑node communication

ISOLATION NOTES

The USB TO RS485 (C) employs an isolated design. The isolation circuitry reduces ground loops and common‑mode interference between the USB host side and the RS485 bus side. The GND on the RS485 side is used as a bus reference ground and for noise immunity; it is not equivalent to directly shorting the field device ground to the computer USB ground.

Isolation and Protection

Isolated RS485 converters are suitable for scenarios where there are significant ground potential differences, many interference sources, long transmission distances, or many bus nodes. The isolation and protection design of the USB TO RS485 (C) includes:

Optical isolation: reduces interference coupling between the USB host side and the RS485 field side
TVS protection: suppresses surge voltages and transient spikes
ESD protection: improves electrostatic discharge immunity during plugging/unplugging, wiring, and on‑site operation
Resettable fuse: automatically recovers after an overcurrent fault, reducing maintenance costs compared to one‑time fuses
120 Ω termination: helps reduce signal reflections in long‑distance or high‑speed communication

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

Method 1: Download Driver Genius from the Internet and let it automatically detect and install the driver.
Method 2: Install the driver manually (the following uses Windows 7 as an example).
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.
Download the software package from the official wiki. Double‑click the application and click Extract:
Click Next:
Check "I accept this agreement", then click Next:
Wait for the installation to complete, then click Finish:
Now check Device Manager; the COM port should be available for normal use.

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-
GND	GND (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.

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

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:

Connect A / B / GND to the Modbus RTU device.
Confirm the slave address, baud rate, parity, data bits, and stop bits.
Use Modbus Poll, a serial debug assistant, or a custom host program to send Modbus RTU commands.
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.