<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">

    System.IO.Ports.SerialPort SerialPort1 = new System.IO.Ports.SerialPort();

    protected void Page_Load(object sender, EventArgs e)
    {
        this.SerialPort1.PortName = "COM1";

        if (!this.SerialPort1.IsOpen)
        {
            this.SerialPort1.Open();
        }

        this.SerialPort1.Write("Hello World");
        this.SerialPort1.Close();
    }

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    </div>
    </form>
</body>
</html>