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----- Original Message -----
From: "Michael Rigby-Jones" <mrjones@NORTELNETWORKS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, August 04, 2000 2:58 AM
Subject: Re: [OT] Using Visual Basic with RS232 Read


> > -----Original Message-----
> > From: Dan Mulally [SMTP:dtcon@RAPIDNET.COM]
> > Sent: Friday, August 04, 2000 1:17 AM
> > To:   PICLIST@MITVMA.MIT.EDU
> > Subject:      [OT] Using Visual Basic with RS232 Read
> >
> > Does anyone have Visual Basic code for reading characters from a PC
serial
> > port. I'm trying to receive data from a PIC. I can see it fine on a
simple
> > communications modem program (Quick Link II is what I've been using) but
> > when I try to read it with visual basic, I get the first few values and
> > then
> > it stops and I get a "run-time error '5'" message on the line which
reads
> > the input buffer. I'm using 9600 baud with about 100msec between
> > characters.
> > I've attached the files if anyone cares to look at them. Thanks in
advance
> > for any help.
> >
> > Dan & Tina Mulally
> > dtcon@rapidnet.com
> > http://rapidnet.com/~dt2000 << File: lloydspc.vbw >>  << File:
> > lloydspc.vbp >>  << File: lloydspc.frm >>
> >
> Couple of points:
>
> 1) The RThreshold property of the comm control is set to zero.  This
> specifies how many characters must be received before firing the OnComm
> event.  Having a value of Zero disables this event from ever happening.
> Instead you seem to be calling the OnComm event directly, effectively
> polling the comm control.  This is bad because the OnComm event gets
called
> not only when you recieve a character, but also for a whole range of Comm
> events (errors, transmission of character etc)  This means you have
> effectively made this Sub re-entrant, i.e. the sub could be called while
you
> are in it.
>
> 2)  Do
>     DoEvents
>     Loop Until MSComm1.InBufferCount >= 1
>     Value = Asc(MSComm1.Input)
>     Select Case MSComm1.CommEvent
>
> What happens if you, say, receive more than one character? The only thing
> that can cause runtime error 5 here is trying to perform an ASC o a null
> string, which shouldn't in theory happen because of your loop, but because
> of point 1), unpredictable things can happen.  You need to buffer the
data,
> either in a string or a byte array.  And use events by setting RThreshold
to
> 1 and read the entire buffer by setting InputLen to 0.  You could read out
> the buffer one character at a time, but I think it's safer to empty the
Comm
> buffer ASAP.
>
> Private Sub MSComm1_OnComm()
>
>    Dim strBuffer as String
>    Dim intCount as Integer
>    Dim bytValue as Byte
>
>     Select Case MSComm1.CommEvent
>     ' Handle each event or error by placing
>     ' code below each case statement
>     ' Errors
>         Case comEventBreak  ' A Break was received.
>                 'Handle your errors here and then Exit Sub.
>     End Select
>
>    If MSComm1.InBufferCount = 0 Then Exit Sub ' ensure we have some
> characters in the buffer
>
>    strBuffer = MSComm1.Input    ' read the conects of the Comm buffer into
a
> string
>    For intCount = 1 To Len(strBuffer)
>       bytValue = Asc(Mid$(strBuffer,intCount,1)
>         DisplayChar(bytBuffer)
>    Next intCount
>
> Exit Sub
>
> Then modify your Display routine so that it does not call the OnComm event
> and remove the polling loop.
>
> Private Sub DisplayChar(Value as Byte)
>
>     If Value = HEADER Then rx_state = 0    'start of packet
>     Select Case rx_state
>         Case 1
>             lblSensor1.Caption = Value
>         Case 2
>             lblSensor2.Caption = Value
>         Case 3
>             lblSensor3.Caption = Value
>         Case 4
>             lblSensor4.Caption = Value
>         Case 5
>             lblSensor5.Caption = Value
>         Case 6
>             lblSensor6.Caption = Value
>         Case 7
>             lblSensor7.Caption = Value
>         Case 8
>             lblSensor8.Caption = Value
>         Case 9
>             lblSensor9.Caption = Value
>         Case 10
>             lblSensor10.Caption = Value
>         Case 11
>             lblSensor11.Caption = Value
>         Case 12
>             lblSensor12.Caption = Value
>         Case 13
>             lblSensor13.Caption = Value
>         Case 14
>             lblSensor14.Caption = Value
>             rx_state = 0
>     End Select
>     rx_state = rx_state + 1
> End Sub
>
> This way the whole serquence of events will be event driven, effectively
> working in the background so that your main program can get on and do
other
> things.  It would also make sense to configure all your labels as a
control
> array., then you could reduce the above code to something like:
>
> Private Sub DisplayChar(Value as Byte)
>
>         If Value = HEADER Then rx_state = 0
>
>         Select Case rx_state
>         Case 1 To 13
>           lblSensor(rx_state).Caption = Value
>         Case 14
>           lblSensor(rx_state).Caption = Value
>           rx_state = 0
>       End Select
>       rx_state = rx_state +1
>
> End Sub
>
> Hope this helps, if you have any more problems email me.
>
> Mike

Thanks Mike,
    I implemented your suggestions as best I could. It seems to work except
for one glitch: If a byte value of zero is sent, the program doesn't seem to
recognize it. It seems that any value from 0 to 255 should be valid. Is
there something unique about 0 when using strings perhaps? Maybe this was
also part of my original problem. I'm also wondering if there is a way to
clear MSComm1.CommEvent which is read only.
    My modified code is attached.
    Thanks for the useful suggestions.

Dan Mulally


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VERSION 5.00
Object = "{648A5603-2C6E-101B-82B6-000000000014}#1.1#0"; "MSCOMM32.OCX"
Begin VB.Form frmForm1
   Caption         =   "Lloyd's Resue Robot"
   ClientHeight    =   5190
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   7440
   LinkTopic       =   "Form1"
   ScaleHeight     =   5190
   ScaleWidth      =   7440
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton cmdClear
      Caption         =   "Clear Errors/Events"
      Height          =   375
      Left            =   5760
      TabIndex        =   35
      Top             =   3480
      Width           =   1575
   End
   Begin MSCommLib.MSComm MSComm1
      Left            =   6600
      Top             =   2400
      _ExtentX        =   1005
      _ExtentY        =   1005
      _Version        =   327680
      DTREnable       =   -1  'True
   End
   Begin VB.CommandButton cmdStop
      Caption         =   "Stop/Exit"
      Height          =   375
      Left            =   1680
      TabIndex        =   1
      Top             =   4560
      Width           =   975
   End
   Begin VB.CommandButton cmdStart
      Caption         =   "Start"
      Height          =   375
      Left            =   240
      TabIndex        =   0
      Top             =   4560
      Width           =   975
   End
   Begin VB.Label Label17
      Caption         =   "RX Header"
      Height          =   255
      Left            =   5280
      TabIndex        =   36
      Top             =   360
      Width           =   855
   End
   Begin VB.Label Label16
      Caption         =   "Serial Port Event"
      Height          =   255
      Left            =   3720
      TabIndex        =   34
      Top             =   4800
      Width           =   1335
   End
   Begin VB.Label Label15
      Caption         =   "Serial Port Error"
      Height          =   255
      Left            =   3720
      TabIndex        =   33
      Top             =   4440
      Width           =   1335
   End
   Begin VB.Label lblEvent
      Caption         =   "No Event"
      Height          =   255
      Left            =   5280
      TabIndex        =   32
      Top             =   4800
      Width           =   1935
   End
   Begin VB.Label lblHeader
      Caption         =   "lblHeader"
      Height          =   255
      Left            =   6360
      TabIndex        =   31
      Top             =   360
      Width           =   855
   End
   Begin VB.Label lblError
      Caption         =   "No Error"
      Height          =   255
      Left            =   5280
      TabIndex        =   30
      Top             =   4440
      Width           =   1935
   End
   Begin VB.Label Label14
      Caption         =   "Sensor 7"
      Height          =   255
      Left            =   120
      TabIndex        =   29
      Top             =   3960
      Width           =   1095
   End
   Begin VB.Label Label13
      Caption         =   "Sensor 6"
      Height          =   255
      Left            =   120
      TabIndex        =   28
      Top             =   3360
      Width           =   1095
   End
   Begin VB.Label Label12
      Caption         =   "Sensor 5"
      Height          =   255
      Left            =   120
      TabIndex        =   27
      Top             =   2760
      Width           =   1095
   End
   Begin VB.Label Label11
      Caption         =   "Sensor 4"
      Height          =   255
      Left            =   120
      TabIndex        =   26
      Top             =   2160
      Width           =   1095
   End
   Begin VB.Label Label10
      Caption         =   "Sensor 3"
      Height          =   255
      Left            =   120
      TabIndex        =   25
      Top             =   1560
      Width           =   1095
   End
   Begin VB.Label Label9
      Caption         =   "Sensor 2"
      Height          =   255
      Left            =   120
      TabIndex        =   24
      Top             =   960
      Width           =   1095
   End
   Begin VB.Label Label8
      Caption         =   "Sensor 1"
      Height          =   255
      Left            =   120
      TabIndex        =   23
      Top             =   360
      Width           =   1095
   End
   Begin VB.Label Label7
      Caption         =   "Left Motor Current"
      Height          =   375
      Left            =   2760
      TabIndex        =   22
      Top             =   3840
      Width           =   1095
   End
   Begin VB.Label Label6
      Caption         =   "Right Motor Current"
      Height          =   375
      Left            =   2760
      TabIndex        =   21
      Top             =   3240
      Width           =   1095
   End
   Begin VB.Label Label5
      Caption         =   "Sensor 12"
      Height          =   255
      Left            =   2760
      TabIndex        =   20
      Top             =   2760
      Width           =   1095
   End
   Begin VB.Label Label4
      Caption         =   "Sensor 11"
      Height          =   255
      Left            =   2760
      TabIndex        =   19
      Top             =   2160
      Width           =   1095
   End
   Begin VB.Label Label3
      Caption         =   "Sensor 10"
      Height          =   255
      Left            =   2760
      TabIndex        =   18
      Top             =   1560
      Width           =   1095
   End
   Begin VB.Label Label2
      Caption         =   "Sensor 9"
      Height          =   255
      Left            =   2760
      TabIndex        =   17
      Top             =   960
      Width           =   1095
   End
   Begin VB.Label Label1
      Caption         =   "Sensor 8"
      Height          =   255
      Left            =   2760
      TabIndex        =   16
      Top             =   360
      Width           =   1095
   End
   Begin VB.Label lblSensor2
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   15
      Top             =   975
      Width           =   1095
   End
   Begin VB.Label lblSensor3
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   14
      Top             =   1605
      Width           =   1095
   End
   Begin VB.Label lblSensor4
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   13
      Top             =   2220
      Width           =   1095
   End
   Begin VB.Label lblSensor5
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   12
      Top             =   2760
      Width           =   1095
   End
   Begin VB.Label lblSensor6
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   11
      Top             =   3360
      Width           =   1095
   End
   Begin VB.Label lblSensor7
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   10
      Top             =   3960
      Width           =   1095
   End
   Begin VB.Label lblSensor1
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   1200
      TabIndex        =   9
      Top             =   360
      Width           =   1095
   End
   Begin VB.Label lblSensor8
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   8
      Top             =   360
      Width           =   1095
   End
   Begin VB.Label lblSensor9
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   7
      Top             =   975
      Width           =   1095
   End
   Begin VB.Label lblSensor10
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   6
      Top             =   1560
      Width           =   1095
   End
   Begin VB.Label lblSensor11
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   5
      Top             =   2160
      Width           =   1095
   End
   Begin VB.Label lblSensor12
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   4
      Top             =   2760
      Width           =   1095
   End
   Begin VB.Label lblSensor13
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   3
      Top             =   3360
      Width           =   1095
   End
   Begin VB.Label lblSensor14
      BackColor       =   &H00FFFFFF&
      Height          =   255
      Left            =   3960
      TabIndex        =   2
      Top             =   3960
      Width           =   1095
   End
End
Attribute VB_Name = "frmForm1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
'--------------------------------------------------------
'Programmer:    Dan Mulally
'Date:          8/7/00
'File:          lloydspc.vbp
'
'This Program runs on a PC and reads the data from the
'robot unit via the base unit using COM1. The unique
'character HEADER signifies the start of the data.
'Subsequent numeric character values are then displayed
'in their label boxes. Errors or other messages are
'displayed in separate label boxes.
'---------------------------------------------------------

Option Explicit
Const HEADER As Byte = 112
    'denotes start of packet, must match robot software
Public Value As Byte
Public rx_state As Byte

Private Sub cmdClear_Click()
    lblError.Caption = "No Errors"
    lblEvent.Caption = "No Events"
End Sub

Private Sub cmdStart_Click()
    Do
    DoEvents
    Call MSComm1_OnComm                    'read serial character
    Loop
End Sub

Private Sub cmdStop_Click()
    MSComm1.PortOpen = False 'disable comm port upon shutdown
    Unload frmForm1
    End
End Sub

Private Sub Form_Load()
    MSComm1.PortOpen = True 'enable comm port upon startup
End Sub

Private Sub MSComm1_OnComm()
    Dim strBuffer As String
    Dim intCount As Integer
    Dim bytValue As Byte

    Select Case MSComm1.CommEvent
    ' Handle each event or error by placing
    ' code below each case statement
    ' Errors
        Case comEventBreak  ' A Break was received.
            lblError.Caption = "Break"
        Case comEventCDTO   ' CD (RLSD) Timeout.
            lblError.Caption = "CD Timeout"
        Case comEventCTSTO  ' CTS Timeout.
            lblError.Caption = "CTS Timeout"
        Case comEventDSRTO  ' DSR Timeout.
            lblError.Caption = "DSR Timeout"
        Case comEventFrame  ' Framing Error
            lblError.Caption = "Frame Error"
        Case comEventOverrun    ' Data Lost.
            lblError.Caption = "Data Lost"
        Case comEventRxOver ' Receive buffer overflow.
            lblError.Caption = "RX Overflow"
        Case comEventRxParity   ' Parity Error.
            lblError.Caption = "Parity Error"
        Case comEventTxFull ' Transmit buffer full.
            lblError.Caption = "TX Full"
        Case comEventDCB    ' Unexpected error retrieving DCB
            lblError.Caption = "DCB Error"
    ' Events
        Case comEvCD    ' Change in the CD line.
            lblEvent.Caption = "CD"
        Case comEvCTS   ' Change in the CTS line.
            lblEvent.Caption = "CTS"
        Case comEvDSR   ' Change in the DSR line.
            lblEvent.Caption = "DSR"
        Case comEvRing  ' Change in the Ring Indicator.
            lblEvent.Caption = "Ring"
        Case comEvReceive   ' Received RThreshold # of
                            ' chars.
            lblEvent.Caption = "RX Thresh#"
        Case comEvSend  ' There are SThreshold number of
                        ' characters in the transmit
                        ' buffer.
            lblEvent.Caption = "SThresh in TX"
        Case comEvEOF   ' An EOF charater was found in
                        ' the input stream
            lblEvent.Caption = "EOF in input"
    End Select
    If MSComm1.InBufferCount = 0 Then Exit Sub
        'ensure we have some characters in the buffer
    strBuffer = MSComm1.Input
        'read contents of the buffer into a string
    For intCount = 1 To Len(strBuffer)
        bytValue = Asc(Mid$(strBuffer, intCount, 1))
        DisplayChar (bytValue)
    Next intCount
    Exit Sub
'    MSComm1.Output = Chr(Value)
End Sub

Public Sub DisplayChar(Value As Byte)
    If Value = HEADER Then
        rx_state = 0    'start of packet
        lblHeader.Caption = Value
    End If
    Select Case rx_state
        Case 1
            lblSensor1.Caption = Value
        Case 2
            lblSensor2.Caption = Value
        Case 3
            lblSensor3.Caption = Value
        Case 4
            lblSensor4.Caption = Value
        Case 5
            lblSensor5.Caption = Value
        Case 6
            lblSensor6.Caption = Value
        Case 7
            lblSensor7.Caption = Value
        Case 8
            lblSensor8.Caption = Value
        Case 9
            lblSensor9.Caption = Value
        Case 10
            lblSensor10.Caption = Value
        Case 11
            lblSensor11.Caption = Value
        Case 12
            lblSensor12.Caption = Value
        Case 13
            lblSensor13.Caption = Value
        Case 14
            lblSensor14.Caption = Value
            rx_state = 0
    End Select
    rx_state = rx_state + 1
End Sub

Private Sub Text1_Change()

End Sub

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