recieving 3 value in uart

[WoF]

The RThreshold should be set to 1. If set to 0 the OnComm() event would never fire.
The code looks good so far. Try it with RThreshold = 1.

[DataMiser]

So I take it that you never hit the break point?

Private Sub MSComm1_OnComm()
Dim p%
Static RLine$
RLine = RLine + MSComm1.Input
p = Instr(RLine, vbCr)  ' Put your break point here and see what you get.
If p Then ' a complete record with three numbers has been received now
dim a$()
a = Split(Left$(RLine,p-1), "/") 'split the line into the three numbers
If UBound(a) = 2 Then
Text1.Text = a(0) 'get first number
Text2.Text = a(1) 'get second number
Text3.Text = a(2) 'get third number
End If
RLine = Mid$(RLine,p+1) 'reset the receiver variable for the next line
End If
End Sub

[feitanx]

I got an error on this line:

"RLine = RLine + MSComm1.Input"

says error reading comm device

the value of P when I breakpoint is 0

[dglienna]

Try this:

RLine = RLine & MSComm1.Input

[DataMiser]

Are you using a real hardware serial port or a usb adapter?

[feitanx]

Still an error in:
"RLine = RLine & MSComm1.Input"

I'am using a Bluetooth serial port profile to connect serially . A Bluetooth module with a serial port profile is used, I connect to the Bluetooth module using a Bluetooth USB dongle.

[dglienna]

Probably aren't even connecting thru the USB. Those can cause problems.

[feitanx]

what do you mean? I can open the port


Please tell me what could be wrong. Please help.

[DataMiser]

the problem is most likely that the on comm event is firing for some reason other than data received and the code is trying to receive data when there is not data hence error reading serial port. Seems like I mentioned this could be a problem a few days ago. See post #7
a simple solution is to do a inbuffer check before trying to read any data from the port.

Add the test just before the input attempt and the corresponding end if at the bottom of the code just before the end sub

e.g.

if MSComm1.InBufferCount>0 then

[DataMiser]

When using the onComm event to handle receiving of data the proper way is to use a case statement. Here is some sample code from MS.

Private Sub MSComm1_OnComm()
         Dim InBuff As String

         Select Case MSComm1.CommEvent
         ' Handle each event or error by placing
         ' code below each case statement.

         ' This template is found in the Example
         ' section of the OnComm event Help topic
         ' in VB Help.

         ' Errors
            Case comEventBreak   ' A Break was received.
            Case comEventCDTO    ' CD (RLSD) Timeout.
            Case comEventCTSTO   ' CTS Timeout.
            Case comEventDSRTO   ' DSR Timeout.
            Case comEventFrame   ' Framing Error.
            Case comEventOverrun ' Data Lost.
            Case comEventRxOver  ' Receive buffer overflow.
            Case comEventRxParity   ' Parity Error.
            Case comEventTxFull  ' Transmit buffer full.
            Case comEventDCB     ' Unexpected error retrieving DCB]

         ' Events
            Case comEvCD   ' Change in the CD line.
            Case comEvCTS  ' Change in the CTS line.
            Case comEvDSR  ' Change in the DSR line.
            Case comEvRing ' Change in the Ring Indicator.
            Case comEvReceive ' Received RThreshold # of chars.
               InBuff = MSComm1.Input
               Call HandleInput(InBuff)            
            Case comEvSend ' There are SThreshold number of
                           ' characters in the transmit buffer.
            Case comEvEOF  ' An EOF character was found in the
                           ' input stream.
         End Select

      End Sub

http://support.microsoft.com/kb/194922

That said testign the InBufferCount as I mentioned will read the data only if data is there which will prevent the error mentioned but as you can see there are several other things that can/will cause the oncomm event to fire.

[WoF]

@DataMiser: Your assumption is wrong.
You can do at ANY time a a$=MSComm1.Input without producing an error, even if the input buffer has no characters. In this case .Input returns an empty string without giving an error.
The reason that RLine = RLine + MSComm1.Input produces an error must lie elsewhere. Port not accessible or something.

@feitanx: First I suggest you change the OnComm like this:

Private Sub MSComm1_OnComm()
  Dim p%
  Static RLine$
  Select Case MSComm1.CommEvent
    Case vbMSCommEvReceive
         RLine = RLine + MSComm1.Input
         p = InStr(RLine, vbCr)  ' Put your break point here and see what you get.
         If p Then ' a complete record with three numbers has been received now
            Dim a$()
            a = Split(Left$(RLine, p - 1), "/") 'split the line into the three numbers
            If UBound(a) = 2 Then
               Text1.Text = a(0) 'get first number
               Text2.Text = a(1) 'get second number
               Text3.Text = a(2) 'get third number
            End If
            RLine = Mid$(RLine, p + 1) 'reset the receiver variable for the next line
         End If
    Case Else
         MsgBox "MSComm event: " + CStr(MSComm1.CommEvent), vbOKOnly, "Error"
  End Select
End Sub

This will only input when a character is received.
Other mscomm events will be notified in a messagebox so as we can see what the error can be.

I think you have to declare the vbMSComm events. The constants do not seem to come automatically when MSComm control is put to the form. So you have to add these private constants:

Private Const vbMSCommEvSend = 1
Private Const vbMSCommEvReceive = 2

on top of your form's code.

[DataMiser]

@DataMiser: Your assumption is wrong.

Actually I got that directly from Microsoft. The error is caused by issuing a read when no data is present to be read. However I did not read far enough. This error happens only with some 3rd party serial drivers such as the one in use here and typically only happens when there is no data present and a read is issued.

[DataMiser]

btw if the port was not accessible the error would appear when an attempt is made to open the port.

[WoF]

Ah, ok. Didn't know that.
When you put an MSComm control on, and have standart serial ports you can read as often as you want from the .Input property without error.

But if this is a third party interface problem the above code will prevent that, beause it does only .Input when the fired event truly is a receive event.

[DataMiser]

On another note while in some or perhaps even many cases you can get away with reading from a port where no data is present it is bad practice to do so. VB let's you get away with a lot but not always. In this case MS says that the serial device must return Success when a read is issued but not all serial devices will do this if there is nothing to read and hence an error whereas if you check the buffer count first the read will not be issued when the buffer is empty and the error should nto occur.