RS485 通信 modbus RTU通信问题，上位机无法读取数据。

[文光山石]

本人用vb.net写了一个上位机软件，就是读不到数据，但是用串口调试程序读得到。
于是我重新用VB.net c# vb6 都写了一个测试通信的小程序，用同一个串口，相同的串口参数（38400,8，N,2 ，串口设置为接收到一个字节就引发事件，二进制格式发送数据） 和下位机，测试发现vb.et 和c#的都不行，vb6的可以正常通信。而且我用两个串口直接对接，一头连接vb.net 测试程序，一头连接串口调试软件，两头收发都正常，c#和vb6这样连接也可以正常通信。就是一头连接测试程序，一头连接下位机，c#和vb.net的都不通，都是可以发送，但是没有任何数据返回，没有触发串口接收数据事件，vb6的就可以正常通信。
难道 .net 的IO.Ports.SerialPort 类有问题，没有vb6的mscomm 控件稳定。
还是我的代码有问题？求大神帮忙分析。
vb.net 主要代码

 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        COM1.BaudRate = 38400
        COM1.DataBits = 8
        COM1.StopBits = 2
        COM1.Parity = IO.Ports.Parity.None

        Dim ports As String() = IO.Ports.SerialPort.GetPortNames() '用SerialPort,获取计算机的有效串口
        Dim port As String
        For Each port In ports
            ComboBox1.Items.Add(port) '向combobox中添加项
        Next port

    End Sub

  Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        '打开串口
        Try
            COM1.PortName = ComboBox1.Text
            COM1.Open()

        Catch ex As Exception
            TextBox2.Text = ex.Message
        End Try
    End Sub

 Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        '发送按钮
        Dim data(20) As Byte
        data(0) = &HA
        data(1) = 1
        data(2) = 3
        data(3) = &HE7

        data(4) = 0
        data(5) = &H27
        data(6) = &HCD
        data(7) = &H18

        Dim a() As String
        a = TextBox1.Text.Split(" ")
        Dim CC As Integer
 
        Try
            data(0) = "&H" & a(0)
            data(1) = "&H" & a(1)
            data(2) = "&H" & a(2)
            data(3) = "&H" & a(3)
            data(4) = "&H" & a(4)
            data(5) = "&H" & a(5)
            Dim HL1 = Get_CRC16(data, 6)
            data(6) = HL1.L
            data(7) = HL1.H


            If COM1.IsOpen = False Then
                TextBox2.Text = "串口未打开"
                Exit Sub
            End If
            CC = 8   '发送字节数
            COM1.Write(data, 0, CC)
            Static i As Integer = 0
            i += 1
            Button3.Text = "发送：" & i
        Catch ex As Exception
            Console.WriteLine(ex.Message)

            TextBox2.Text = ex.Message

        End Try
    End Sub

 Private Sub COM1_DataReceived(sender As Object, e As IO.Ports.SerialDataReceivedEventArgs) Handles COM1.DataReceived
        '接收事件
        Static cccc As Integer = 1
        cm("接收：" & cccc)
        cccc += 1
        Dim InBytes() As Byte   '读数据BUFF
        Dim readCount As Integer

        ReDim InBytes(105 - 1)  ' ReDim InBytes(105 - 1)

        Dim tmpcount As Integer = InBytes.Length   '定长

        If tmpcount > 50 Then
            Delay_DoEvents(20 + 30)    '延迟以接收数据
        End If
        readCount = COM1.Read(InBytes, 0, tmpcount)
        COM1.DiscardInBuffer()
        showdata(InBytes)   '显示到文本框
    End Sub

C#主要代码

 private void Form1_Load(object sender, EventArgs e)
        {
            this.COM1.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(COM1_DataReceived);
            this.COM1.BaudRate = 38400;
            this.COM1.DataBits = 8;
            this.COM1.StopBits = StopBits.Two;
            this.COM1.Parity = Parity.None;
            String[] ports = System.IO.Ports.SerialPort.GetPortNames();// 用SerialPort,获取计算机的有效串口
            //  String port;
            foreach (String port in ports)
            {
                comboBox1.Items.Add(port);//'向combobox中添加项
            }
        }

       private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                this.COM1.PortName = this.comboBox1.Text;
                this.COM1.Open();
            }
            catch (Exception ex)
            {
                this.textBox2.Text = ex.Message;
            }
        }

       private void button3_Click(object sender, EventArgs e)
        {
            int num;
            int num3;
            byte[] buffer = new byte[0x15]; 
            string[] strArray = this.textBox1.Text.Split(new char[] { ' ' });
            try
            {
                buffer[0] = Convert.ToByte(strArray[0], 16);
                buffer[1] = Convert.ToByte(strArray[1], 16);
                buffer[2] = Convert.ToByte(strArray[2], 16);
                buffer[3] = Convert.ToByte(strArray[3], 16);
                buffer[4] = Convert.ToByte(strArray[4], 16);
                buffer[5] = Convert.ToByte(strArray[5], 16);
                HL hl = this.Get_CRC16(buffer, 6);
                buffer[6] = hl.L;
                buffer[7] = hl.H;
                this.COM1.Write(buffer, 0, 8); //发送8个字节
                c++;
                this.button3.Text = "发送 " + c;
            }
            catch (Exception exception1)
            {
                this.textBox2.Text = exception1.Message;
            }
        }

   private void COM1_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            byte[] buffer = new byte[0x69];
            int length = buffer.Length;
            if (length > 50)
            {
                this.Delay_DoEvents(50L);//延迟
            }
            int num = this.COM1.Read(buffer, 0, length);
            this.COM1.DiscardInBuffer();
            this.showdata(buffer);//显示数据
        }

vb6的跟vb.net 代码差不多就是控件不一样。

[lylkr]

上位机如果是usb转串口，换成板载或扩展卡扩展，或vb.net里用vb6.0的串口控件 c#没用过 vb.net我也碰到过类似情况，就是真么解决的

[菜鸟中的菜鸟大神]

If COM1.IsOpen = False Then
                TextBox2.Text = "串口未打开"
                Exit Sub
            End If

这句我觉得放Load事件比较好吧。然后在打开串口里设置textbox2.text="串口已连接" 发送按钮我觉得该这样：

try
  if com1.isopen=true then
    …………（date(0-7)）
     CC = 8   '发送字节数
            COM1.Write(data, 0, CC)
            Static i As Integer = 0
            i += 1
            Button3.Text = "发送：" & i
        Catch ex As Exception
            Console.WriteLine(ex.Message)
 
            TextBox2.Text = ex.Message
 
        End Try