'-------------------------------------------------------------------------------
' CommRead - Read serial port input buffer.
'
' Parameters:
' intPortID - Port ID used when port was opened.
' strData - Data buffer.
' lngSize - Maximum number of bytes to be read.
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommRead(intPortID As Integer, strData As String, _
lngSize As Long) As Long

Dim lngStatus As Long
Dim lngRdSize As Long, lngBytesRead As Long
Dim lngRdStatus As Long, strRdBuffer As String * 4096
Dim lngErrorFlags As Long, udtCommStat As COMSTAT

On Error GoTo Routine_Error

strData = ""
lngBytesRead = 0
DoEvents

' Clear any previous errors and get current status.
lngStatus = ClearCommError(udtPorts(intPortID).lngHandle, lngErrorFlags, _
udtCommStat)

If lngStatus = 0 Then
lngBytesRead = -1
lngStatus = SetCommError("CommRead (ClearCommError)")
GoTo Routine_Exit
End If

If udtCommStat.cbInQue > 0 Then
If udtCommStat.cbInQue > lngSize Then
lngRdSize = udtCommStat.cbInQue
Else
lngRdSize = lngSize
End If
Else
lngRdSize = 0
End If

If lngRdSize Then
lngRdStatus = ReadFile(udtPorts(intPortID).lngHandle, strRdBuffer, _
lngRdSize, lngBytesRead, udtCommOverlap)

If lngRdStatus = 0 Then
lngStatus = GetLastError
If lngStatus = ERROR_IO_PENDING Then
' Wait for read to complete.
' This function will timeout according to the
' COMMTIMEOUTS.ReadTotalTimeoutConstant variable.
' Every time it times out, check for port errors.

' Loop until operation is complete.
While GetOverlappedResult(udtPorts(intPortID).lngHandle, _
udtCommOverlap, lngBytesRead, True) = 0

lngStatus = GetLastError

If lngStatus <> ERROR_IO_INCOMPLETE Then
lngBytesRead = -1
lngStatus = SetCommErrorEx( _
"CommRead (GetOverlappedResult)", _
udtPorts(intPortID).lngHandle)
GoTo Routine_Exit
End If
Wend
Else
' Some other error occurred.
lngBytesRead = -1
lngStatus = SetCommErrorEx("CommRead (ReadFile)", _
udtPorts(intPortID).lngHandle)
GoTo Routine_Exit

End If
End If

strData = Left$(strRdBuffer, lngBytesRead)
End If

Routine_Exit:
CommRead = lngBytesRead
Exit Function

Routine_Error:
lngBytesRead = -1
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommRead"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function