Unsure on proper use of Serial Port Data Received Event - vb.net

Question

I'm working on a VSTO add-in for Excel 2013 in VB.NET that will help me interface with an instrument via a serial connection. I currently have the COM connection set up correctly and it will allow me to send and receive one command at a time. I'd like to set it up so that I can push one button and have it collect two separate readings in different worksheet cells. Using the code below, the tools work great to collect a single reading, but when I enable the code to send a second command to the instrument the Data Received event stops working entirely until I send another single read command. I know that the instrument received and processed the second command, but it never appears in excel. Could anyone help with a way to modify this code?
Private Sub mySerialPort_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
'Handles serial port data received events
UpdateFormDeligate1 = New UpdateFormDeligate(AddressOf UpdateDisplay)
Dim n As Integer = mySerialPort.BytesToRead 'find number of bytes in buff
comBuffer = New Byte(n - 1) {} 're-dimension storage buffer (n - 1)
mySerialPort.Read(comBuffer, 0, n) 'read data from the buffer
comBuffer2 = mySerialPort.ReadTo(vbCr)
Me.Invoke(UpdateFormDeligate1) 'call the deligate
mySerialPort.Close()
End Sub
Private Sub Invoke(updateFormDeligate1 As UpdateFormDeligate)
lblReading.Label = processReading() 'write to a Current Reading lable on the ribbon
Dim myApp As Excel.Application = Globals.ThisAddIn.Application
Dim currentCell = myApp.ActiveCell
currentCell.Value = processReading() 'write data in the excel active cell
Try
advanceCell()
Catch ex As Exception
System.Windows.Forms.MessageBox.Show(ex.Message)
End Try
If measureNo = 2 Then 'this case is selected when I want to read 2 measurements with a single button push
cmdSent = 2
sendCommand(measureCmd)
End If
End Sub
Private Sub UpdateDisplay()
End Sub
Note that I did not include my sendCommand sub because this is a simple .write command to the instrument that appears to be working correctly in all cases. I'd much appreciate any help anyone could provide as I'm pretty new to using data received events.

Answer 1

OK, I tried to isolate only the relevant the part of the script that was having an issue and I created a completely new toolbar for testing. Below is the full code for this new toolbar that contains one connect/measure button and a label that displays the status/result. I tried to comment the code to make it readable, hopefully this helps.
This new toolbar does appear to be working correctly. I'm still a little unsure on my correct usage of the DataReceived event handler in conjunction with the Invoke method (which Visual Studio slightly changed for use with Excel2013). Could anyone please provide comment as to whether I'm still using these events in an unclear way and provide a suggestion on how I may make it better?
Thanks again in advance for any help. I really appreciate it.
Imports Microsoft.Office.Tools.Ribbon
Imports System.IO.Ports
Public Class Measure2x_COM
Dim mySerialPort As New SerialPort
Dim CMD As String = "M" & vbCr 'statement telling instrument to measure
Dim measureNo As Integer = 0 'counts the number of measure commands sent to the instrument
Private Delegate Sub UpdateFormDeligate()
Private UpdateFormDeligate1 As UpdateFormDeligate
Dim sngReading As Single 'this is the reading received from the instrument as a single data type
Private Sub setupConnectCOM()
'Open COM and send measure command - this part works correctly
'first, check if serial port is open
If mySerialPort.IsOpen Then 'send measure command
mySerialPort.Write(CMD) 'the instrument will generally take 15.1 sec to perform a measurement before sending the result back
Else
'if serial port is not open, set it up, then open, then send command
'Setup COM --this part works correctly
With mySerialPort
.PortName = "COM3"
.BaudRate = 1200
.DataBits = 7
.Parity = Parity.None
.StopBits = StopBits.Two
.Handshake = Handshake.None
.ReadTimeout = 16000
End With
Try
mySerialPort.Open()
Catch ex As Exception
System.Windows.Forms.MessageBox.Show(ex.Message)
Exit Sub 'exit sub if the connection fails
End Try
Threading.Thread.Sleep(200) 'wait 0.2 sec for port to open
mySerialPort.Write(CMD) 'send measure command after serial port is open
End If
measureNo = 1
lblResult.Label = "Measuring"
End Sub
Private Sub Measure2x_COM_Load(ByVal sender As System.Object, ByVal e As RibbonUIEventArgs) Handles MyBase.Load
AddHandler mySerialPort.DataReceived, AddressOf mySerialPort_DataReceived
End Sub
Private Sub mySerialPort_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
'Handles serial port data received events
UpdateFormDeligate1 = New UpdateFormDeligate(AddressOf UpdateDisplay)
'Read data as it comes back from serial port
'I had to do this in two steps because it, for some reason needs to read
'the +/- symbol as a Byte, then needs to read the ASCII measurement number
'the third part concatenates the data and converts it to a single type
'part 1 - read +/- symbol
Dim comBuffer As Byte()
Dim n As Integer = mySerialPort.BytesToRead 'find number of bytes in buff
comBuffer = New Byte(n - 1) {} 're-dimension storage buffer (n - 1)
mySerialPort.Read(comBuffer, 0, n) 'read data from the buffer
'part 2 - read ASCII measurement number
Dim comBuffer2 As String
comBuffer2 = mySerialPort.ReadTo(vbCr)
'part 3 - concatenate read data and convert to single type
Dim txtReading As String = Nothing
txtReading = System.Text.ASCIIEncoding.ASCII.GetString(comBuffer) & CStr(CInt(comBuffer2) / 10)
sngReading = CSng(txtReading)
'Call the update form deligate
'Visual Studio slightly changed this from the example on Microsoft's website that used a Windows Form
'I tried the code in a windows form and I get the same results
Me.Invoke(UpdateFormDeligate1) 'call the deligate
End Sub
Private Sub Invoke(updateFormDeligate1 As UpdateFormDeligate)
lblResult.Label = sngReading 'set the Result label in the ribbon to equal the received data value
'now place the data received in the active cell in the worksheet
Dim myApp As Excel.Application = Globals.ThisAddIn.Application
Dim currentCell = myApp.ActiveCell
currentCell.Value = sngReading
'advance cell to the next cell
Dim newCell = currentCell
newCell = myApp.ActiveCell.Offset(1, 0)
newCell.Select()
currentCell = newCell
'check if this was the first reading from the instrument
'if it was the first reading, then send a second read command
If measureNo = 1 Then
measureNo = 2 'make sure to change measurement number to 2 to avoid infinite loop
mySerialPort.Write(CMD) 'send command to measure to instrument
End If
End Sub
'the usage of this section changed from the Microsoft Windows Form example
'in function, the mySerialPort_DataREceived(), Invoke(), and UpdateDisplay() functions do appear to be
'working with the same results and same hangups
Private Sub UpdateDisplay()
End Sub
Private Sub btnMeasure_Click(sender As Object, e As RibbonControlEventArgs) Handles btnMeasure.Click
setupConnectCOM() 'connect to COM and send first measure command
End Sub
End Class