how to read usb data like serial port?

Reading data from a USB device that uses a CH340 chip is straightforward because these devices emulate a standard serial port. This means you can use the built-in SerialPort class in C# to read and write bytes, just as you would with a physical serial port.

https://learn.microsoft.com/en-us/dotnet/api/system.io.ports.serialport?view=net-9.0-pp

Using the SerialPort Class

The following code example demonstrates how to establish a connection and read data from a COM port. This assumes your device is connected and its driver has assigned it a COM port number (e.g., COM3) in Windows.

using System.IO.Ports;
using System;
// Replace "COM3" with the actual COM port of your device.
string portName = "COM3";
try
{
    // Initialize a new instance of the SerialPort class with the specified port and baud rate.
    // The baud rate (e.g., 9600) must match the settings of your device.
    using (SerialPort serialPort = new SerialPort(portName, 9600))
    {
        // Open the serial port connection.
        serialPort.Open();
        Console.WriteLine($"Serial port {portName} opened. Reading data...");
        // Continuously read data from the port.
        while (true)
        {
            // You can read the data as a string until a newline character is received.
            string line = serialPort.ReadLine();
            Console.WriteLine($"Received line: {line}");
            // Alternatively, read raw bytes if your protocol doesn't use newlines.
            int bytesToRead = serialPort.BytesToRead;
            if (bytesToRead > 0)
            {
                byte[] buffer = new byte[bytesToRead];
                int bytesRead = serialPort.Read(buffer, 0, bytesToRead);
                Console.WriteLine($"Received {bytesRead} bytes: {BitConverter.ToString(buffer)}");
            }
        }
    }
}
catch (Exception ex)
{
    Console.WriteLine($"Error: {ex.Message}");
}

Handling Data Packets

Most devices that communicate via a serial port follow a specific protocol. This protocol defines how data is structured into packets, often with start and end bytes, a payload, and a checksum.

You'll need to write additional code to correctly frame these packets. This involves:

Identifying a start byte: Reading bytes until you find the start of a packet.

Reading the payload: Reading the specified number of bytes for the data itself.

Verifying the packet: Checking for a checksum or end byte to ensure the packet was received correctly and completely.

Without implementing this logic, you'll simply be receiving a stream of bytes, not the meaningful data packets your device is sending.