My C# program can't receive any data from Xiao

Products & Technology
#1

I started with a simple sketch to send data back to PC, also allow PC to control the LEDs on xiao.

When running the sketch, if I use teraterm/putty, i can receive data from xiao and control the LED.

but when i use c#, i can control the LED, but i can never receive anything from xiao. Any suggestion?

Thanks for any pointer!

[xiao sketch]

  const int LedPin = 13;  
  int ledState = 0;  

  void setup()  
  {   
    pinMode(LedPin, OUTPUT);  
    SerialUSB.begin(9600);    
  }  

  void loop()  
  {   
    char receiveVal;     
    SerialUSB.print('1');
    delay(200);
  
    if(SerialUSB.available() > 0)  
    {          
        receiveVal = SerialUSB.read();  
        if(receiveVal == '1')      
          ledState = 1;     
        else  
          ledState = 0; 
    }     
  
    digitalWrite(LedPin, ledState);   
  }

[VS2017 C# console program]

  using System;
  using System.IO.Ports;
  namespace ConsoleApp1
  {
      class Program
      {
          static SerialPort _serialPort;
          static char [] message = new char [6000];
          public static void Main()
          {
              int i;
              _serialPort = new SerialPort();
              _serialPort.PortName = "COM6";//Set your board COM
              _serialPort.BaudRate = 9600;
              _serialPort.Open();
              while (true)
              {
                  if ((i=_serialPort.BytesToRead)>0)
                  {
                      _serialPort.Read(message, 0, i);
                      Console.WriteLine("Read="+i.ToString());
                  }
                  if (Console.KeyAvailable)
                  {
                      string c = Console.ReadLine();
                      _serialPort.Write(c);
                      if (c == "x")
                      {
                          _serialPort.Close();
                          return;
                      }
                  }
              }
          }
      }
  }