如何从 com 端口读取单个字符

Question

thank you for looking over my question. I'm trying to read from a COM port. I have a launchpad microcontroller and I've already made it so I can send single character codes to it and have the microcontroller respond accordingly. Here's the application as it is currently:

Current Application

I can currently make pins go high and low to my hearts content. However, I would like to a Read pin value from the controller. I made a subroutine that opens up the com port and sends the character that causes the a pin to go high or low .

The code on the microcontroller is setup so that if it gets the 'T' character it sends a single character back immediately. How do I retrieve this single character from the com port?

I'm new to vb.net, so be gentle. The code is below for reference. I open and close the com port to send data using the sendCom() function. I would like to have a readCom() function that would grb my character if possible.

Thanks for looking over my dilemma.

~Triston

/------------------------------------ Code for reference ------------------------------------------------

Public Class Form1
Dim myBtn0 As Boolean
Dim myBtn1 As Boolean
Dim myBtn2 As Boolean
Dim myBtn3 As Boolean
Dim myBtn4 As Boolean
Dim myBtn5 As Boolean
Dim myBtn6 As Boolean
Dim myBtn7 As Boolean


Function sendCom(ByVal Data As Char)
    Dim myCom As System.IO.Ports.SerialPort
    myCom = My.Computer.Ports.OpenSerialPort("COM6", 9600, 0, 8)

    myCom.Write(Data)
    myCom.Close()
    myCom.Dispose()
End Function


Function pinFlip(ByVal pinNum As Integer, ByVal pState As Boolean) As Integer
    InfoBox.Clear()
    InfoBox.Multiline = True
    Select Case pinNum
        Case 0
            If pState Then
                InfoBox.AppendText("C" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("c" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 1
            If pState Then
                InfoBox.AppendText("D" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("d" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 2
            If pState Then
                InfoBox.AppendText("E" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("e" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 3
            If pState Then
                InfoBox.AppendText("F" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("f" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 4
            If pState Then
                InfoBox.AppendText("G" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("g" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 5
            If pState Then
                InfoBox.AppendText("H" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("h" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 6
            If pState Then
                InfoBox.AppendText("I" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("i" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
        Case 7
            If pState Then
                InfoBox.AppendText("J" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            Else
                InfoBox.AppendText("j" + Environment.NewLine)
                InfoBox.ScrollToCaret()
            End If
    End Select

End Function
Private Sub GetPorts_Click(sender As Object, e As EventArgs) Handles GetPorts.Click
    ' Show all available COM ports.
    ListBox1.Items.Clear()
    For Each sp As String In My.Computer.Ports.SerialPortNames
        ListBox1.Items.Add(sp)
    Next
End Sub

Private Sub Send_Click(sender As Object, e As EventArgs) Handles Send.Click

    Dim Data As Char
    'Dim Com6 As System.IO.Ports.SerialPort
    'Com6 = My.Computer.Ports.OpenSerialPort("COM5", 9600, 0, 8)
    Data = "A"
    'Com6.Open()

    'System.Threading.Thread.Sleep(200)
    'Com6.Write(Data)
    'System.Threading.Thread.Sleep(200)
    'Com6.Close()
    'System.Threading.Thread.Sleep(200)
    'Com6.Dispose()
    sendCom(Data)
    P0.BackColor = Color.Green
    P1.BackColor = Color.Green
    P2.BackColor = Color.Green
    P3.BackColor = Color.Green
    P4.BackColor = Color.Green
    P5.BackColor = Color.Green
    P6.BackColor = Color.Green
    P7.BackColor = Color.Green

    myBtn0 = True
    myBtn1 = True
    myBtn2 = True
    myBtn3 = True
    myBtn4 = True
    myBtn5 = True
    myBtn6 = True
    myBtn7 = True

    InfoBox.Clear()
    InfoBox.Multiline = True
    InfoBox.AppendText("All Set High" + Environment.NewLine)
    InfoBox.ScrollToCaret()
End Sub

Private Sub SendB_Click(sender As Object, e As EventArgs) Handles SendB.Click
    Dim Data As Char
    'Dim Com6 As System.IO.Ports.SerialPort
    'Com6 = My.Computer.Ports.OpenSerialPort("COM5", 9600, 0, 8)
    'Com6.Open()
    Data = "B"
    ' Send strings to a serial port.
    'System.Threading.Thread.Sleep(200)
    'Com6.Write(Data)
    'System.Threading.Thread.Sleep(200)
    'Com6.Close()
    'System.Threading.Thread.Sleep(200)
    'Com6.Dispose()
    sendCom(Data)
    P0.BackColor = Color.Red
    P1.BackColor = Color.Red
    P2.BackColor = Color.Red
    P3.BackColor = Color.Red
    P4.BackColor = Color.Red
    P5.BackColor = Color.Red
    P6.BackColor = Color.Red
    P7.BackColor = Color.Red

    myBtn0 = False
    myBtn1 = False
    myBtn2 = False
    myBtn3 = False
    myBtn4 = False
    myBtn5 = False
    myBtn6 = False
    myBtn7 = False

    InfoBox.Clear()
    InfoBox.Multiline = True
    InfoBox.AppendText("All Set Low" + Environment.NewLine)
    InfoBox.ScrollToCaret()
End Sub
Private Sub myRead_Click(sender As Object, e As EventArgs) Handles myRead.Click
    InfoBox.Clear()
    InfoBox.Multiline = True
    InfoBox.AppendText("The READ!" + Environment.NewLine)
    InfoBox.ScrollToCaret()
End Sub
Private Sub PortInfo_Click(sender As Object, e As EventArgs) Handles PortInfo.Click
    Dim Com6 As System.IO.Ports.SerialPort
    Dim myData As String
    InfoBox.Clear()
    InfoBox.Multiline = True
    Com6 = My.Computer.Ports.OpenSerialPort("COM6", 9600, 0, 8)
    myData = "Port Name: " + CStr(Com6.PortName)
    InfoBox.AppendText(myData + Environment.NewLine)
    InfoBox.ScrollToCaret()
    myData = "BaudRate: " + CStr(Com6.BaudRate)
    InfoBox.AppendText(myData + Environment.NewLine)
    InfoBox.ScrollToCaret()
    myData = "Parity: " + CStr(Com6.Parity)
    InfoBox.AppendText(myData + Environment.NewLine)
    InfoBox.ScrollToCaret()
    myData = "Data Width: " + CStr(Com6.DataBits)
    InfoBox.AppendText(myData + Environment.NewLine)
    InfoBox.ScrollToCaret()
    myData = "Stop Bits: " + CStr(Com6.StopBits)
    InfoBox.AppendText(myData + Environment.NewLine)
    InfoBox.ScrollToCaret()
    Com6.Dispose()

End Sub

Private Sub Btn0_Click(sender As Object, e As EventArgs) Handles Btn0.Click
    Select Case myBtn0
        Case False
            P0.BackColor = Color.Green
            myBtn0 = True
            sendCom("C")
        Case True
            P0.BackColor = Color.Red
            myBtn0 = False
            sendCom("K")
    End Select

    pinFlip(0, myBtn0)
End Sub

Private Sub Btn1_Click(sender As Object, e As EventArgs) Handles Btn1.Click
    Select Case myBtn1
        Case False
            P1.BackColor = Color.Green
            myBtn1 = True
            sendCom("D")
        Case True
            P1.BackColor = Color.Red
            myBtn1 = False
            sendCom("L")
    End Select
    pinFlip(1, myBtn1)
End Sub

Private Sub Btn2_Click(sender As Object, e As EventArgs) Handles Btn2.Click
    Select Case myBtn2
        Case False
            P2.BackColor = Color.Green
            myBtn2 = True
            sendCom("E")
        Case True
            P2.BackColor = Color.Red
            myBtn2 = False
            sendCom("M")
    End Select
    pinFlip(2, myBtn2)
End Sub

Private Sub Btn3_Click(sender As Object, e As EventArgs) Handles Btn3.Click
    Select Case myBtn3
        Case False
            P3.BackColor = Color.Green
            myBtn3 = True
            sendCom("F")
        Case True
            P3.BackColor = Color.Red
            myBtn3 = False
            sendCom("N")
    End Select
    pinFlip(3, myBtn3)
End Sub

Private Sub Btn4_Click(sender As Object, e As EventArgs) Handles Btn4.Click
    Select Case myBtn4
        Case False
            P4.BackColor = Color.Green
            myBtn4 = True
            sendCom("G")
        Case True
            P4.BackColor = Color.Red
            myBtn4 = False
            sendCom("O")
    End Select
    pinFlip(4, myBtn4)
End Sub

Private Sub Btn5_Click(sender As Object, e As EventArgs) Handles Btn5.Click
    Select Case myBtn5
        Case False
            P5.BackColor = Color.Green
            myBtn5 = True
            sendCom("H")
        Case True
            P5.BackColor = Color.Red
            myBtn5 = False
            sendCom("P")
    End Select
    pinFlip(5, myBtn5)
End Sub

Private Sub Btn6_Click(sender As Object, e As EventArgs) Handles Btn6.Click
    Select Case myBtn6
        Case False
            P6.BackColor = Color.Green
            myBtn6 = True
            sendCom("I")
        Case True
            P6.BackColor = Color.Red
            myBtn6 = False
            sendCom("Q")
    End Select
    pinFlip(6, myBtn6)
End Sub

Private Sub Btn7_Click(sender As Object, e As EventArgs) Handles Btn7.Click
    Select Case myBtn7
        Case False
            P7.BackColor = Color.Green
            myBtn7 = True
            sendCom("J")
        Case True
            P7.BackColor = Color.Red
            myBtn7 = False
            sendCom("R")
    End Select
    pinFlip(7, myBtn7)
End Sub

End Class

Answer 1

Your function sendCom(ByVal Data As Char) opens the COM port, then sends data, then closes it, never keeping it open for receiving data. This is fine if you want to poll for received data and timeout if there is none. See the example here for the receive function that you need to add to your code.