serial data help please

Hello everyone:
I am new to Visual Basic and I have a problem that I cannot put my finger on. I am working on a school project and I am getting some serial data from a microprocessor. I have designed my "Do" loop to wait for each data set coming in at intervals of about 1/2 a second from the microprocessor.

When I comment the following lines:

bufferVar = ""
myBufferData = ""
myDataString = ""

in my code below I get the correct serial data set the first time around and after that it repeats the same data in the textbox however many times determined by the "for" loop with only one serial data delay (1/2 a second). BUT if I uncomment these lines I only get the last data set once after the correct delay determined by the for loop. So, if I have 6 serial data sets my program will run for 3 seconds and display only the last data set.

What I would like it to do is to print each data set as it arrives for a long period of time. Any Ideas? Thanks in advance.

Here is my code:

Private Sub Command1_Click(Index As Integer)

'setup the port
If MSComm1.PortOpen = False Then MSComm1.CommPort = 5
MSComm1.Settings = "9600,N,8,1"
MSComm1.PortOpen = True
MSComm1.InputMode = comInputModeText

For i = 1 To 3
'reset data to enter clean every time
'endFlag used to find out when buffer has one full data set
endFlag = False
'MSComm1.InBufferCount = 0 to start with empty buffer every time
MSComm1.InBufferCount = 0
'start clean every time to extract serial data
'OK, if I comment these three variables I get only the first serial data set
'repeated however many times is indicated in the "for" loop
'BUT, if I uncomment these three variables I get only the last data set
'with the correct delay (1/2 a sec per iteration of "for" loop)
bufferVar = ""
myBufferData = ""
myDataString = ""

setEnd = 0

'loops until "last item" marker is found
'and sets location value to setEnd
Do
myBufferData = myBufferData & MSComm1.Input
endFlag = InStr(myBufferData, ",")
Loop Until endFlag = True

'locates last item marker on data set
setEnd = InStr(myBufferData, ",")

'gets location markers for x, y and z
xPos = InStr(myBufferData, "x")
yPos = InStr(myBufferData, "y")
zPos = InStr(myBufferData, "z")

'builds buffer data set string
'used to print the variable locations to the screen, not important
bufferVar = bufferVar & "xPos = " & xPos & vbCrLf
bufferVar = bufferVar & "yPos = " & yPos & vbCrLf
bufferVar = bufferVar & "zPos = " & zPos & vbCrLf
bufferVar = bufferVar & "setEnd = " & setEnd & vbCrLf

myDataString = myDataString & "x = " & Mid(myBufferData, (xPos + 1), (yPos - xPos - 1)) & " "
myDataString = myDataString & "y = " & Mid(myBufferData, (yPos + 1), (zPos - yPos - 1)) & " "
myDataString = myDataString & "z = " & Mid(myBufferData, (zPos + 1), (setEnd - zPos - 1)) & vbCrLf

'write to textBoxes
txtData.Text = myDataString
txtBuffer.Text = bufferVar

Next i

'when done close com port
If MSComm1.PortOpen = True Then MSComm1.PortOpen = False
End Sub