Collection of COM port communications in Excel

http://dev.emcelettronica.com/serial-port-communication-in-excel-vba


Option Explicit

'-------------------------------------------------------------------------------

'
' This VB module is a collection of routines to perform serial port I/O without
' using the Microsoft Comm Control component. This module uses the Windows API
' to perform the overlapped I/O operations necessary for serial communications.
'
' The routine can handle up to 4 serial ports which are identified with a
' Port ID.
'
' All routines (with the exception of CommRead and CommWrite) return an error
' code or 0 if no error occurs. The routine CommGetError can be used to get
' the complete error message.
'-------------------------------------------------------------------------------

'-------------------------------------------------------------------------------
' Public Constants
'-------------------------------------------------------------------------------

' Output Control Lines (CommSetLine)
Const LINE_BREAK = 1
Const LINE_DTR = 2
Const LINE_RTS = 3

' Input Control Lines (CommGetLine)
Const LINE_CTS = &H10&
Const LINE_DSR = &H20&
Const LINE_RING = &H40&
Const LINE_RLSD = &H80&
Const LINE_CD = &H80&

'-------------------------------------------------------------------------------
' System Constants
'-------------------------------------------------------------------------------
Private Const ERROR_IO_INCOMPLETE = 996&
Private Const ERROR_IO_PENDING = 997
Private Const GENERIC_READ = &H80000000
Private Const GENERIC_WRITE = &H40000000
Private Const FILE_ATTRIBUTE_NORMAL = &H80
Private Const FILE_FLAG_OVERLAPPED = &H40000000
Private Const FORMAT_MESSAGE_FROM_SYSTEM = &H1000
Private Const OPEN_EXISTING = 3

' COMM Functions
Private Const MS_CTS_ON = &H10&
Private Const MS_DSR_ON = &H20&
Private Const MS_RING_ON = &H40&
Private Const MS_RLSD_ON = &H80&
Private Const PURGE_RXABORT = &H2
Private Const PURGE_RXCLEAR = &H8
Private Const PURGE_TXABORT = &H1
Private Const PURGE_TXCLEAR = &H4

' COMM Escape Functions
Private Const CLRBREAK = 9
Private Const CLRDTR = 6
Private Const CLRRTS = 4
Private Const SETBREAK = 8
Private Const SETDTR = 5
Private Const SETRTS = 3

'-------------------------------------------------------------------------------
' System Structures
'-------------------------------------------------------------------------------
Private Type COMSTAT
fBitFields As Long ' See Comment in Win32API.Txt
cbInQue As Long
cbOutQue As Long
End Type

Private Type COMMTIMEOUTS
ReadIntervalTimeout As Long
ReadTotalTimeoutMultiplier As Long
ReadTotalTimeoutConstant As Long
WriteTotalTimeoutMultiplier As Long
WriteTotalTimeoutConstant As Long
End Type

'
' The DCB structure defines the control setting for a serial
' communications device.
'
Private Type DCB
DCBlength As Long
BaudRate As Long
fBitFields As Long ' See Comments in Win32API.Txt
wReserved As Integer
XonLim As Integer
XoffLim As Integer
ByteSize As Byte
Parity As Byte
StopBits As Byte
XonChar As Byte
XoffChar As Byte
ErrorChar As Byte
EofChar As Byte
EvtChar As Byte
wReserved1 As Integer 'Reserved; Do Not Use
End Type

Private Type OVERLAPPED
Internal As Long
InternalHigh As Long
offset As Long
OffsetHigh As Long
hEvent As Long
End Type

Private Type SECURITY_ATTRIBUTES
nLength As Long
lpSecurityDescriptor As Long
bInheritHandle As Long
End Type

'-------------------------------------------------------------------------------
' System Functions
'-------------------------------------------------------------------------------
'
' Fills a specified DCB structure with values specified in
' a device-control string.
'
Private Declare Function BuildCommDCB Lib "kernel32" Alias "BuildCommDCBA" _
(ByVal lpDef As String, lpDCB As DCB) As Long
'
' Retrieves information about a communications error and reports
' the current status of a communications device. The function is
' called when a communications error occurs, and it clears the
' device's error flag to enable additional input and output
' (I/O) operations.
'
Private Declare Function ClearCommError Lib "kernel32" _
(ByVal hFile As Long, lpErrors As Long, lpStat As COMSTAT) As Long
'
' Closes an open communications device or file handle.
'
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
'
' Creates or opens a communications resource and returns a handle
' that can be used to access the resource.
'
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" _
(ByVal lpFileName As String, ByVal dwDesiredAccess As Long, _
ByVal dwShareMode As Long, lpSecurityAttributes As Any, _
ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, _
ByVal hTemplateFile As Long) As Long
'
' Directs a specified communications device to perform a function.
'
Private Declare Function EscapeCommFunction Lib "kernel32" _
(ByVal nCid As Long, ByVal nFunc As Long) As Long
'
' Formats a message string such as an error string returned
' by anoher function.
'
Private Declare Function FormatMessage Lib "kernel32" Alias "FormatMessageA" _
(ByVal dwFlags As Long, lpSource As Any, ByVal dwMessageId As Long, _
ByVal dwLanguageId As Long, ByVal lpBuffer As String, ByVal nSize As Long, _
Arguments As Long) As Long
'
' Retrieves modem control-register values.
'
Private Declare Function GetCommModemStatus Lib "kernel32" _
(ByVal hFile As Long, lpModemStat As Long) As Long
'
' Retrieves the current control settings for a specified
' communications device.
'
Private Declare Function GetCommState Lib "kernel32" _
(ByVal nCid As Long, lpDCB As DCB) As Long
'
' Retrieves the calling thread's last-error code value.
'
Private Declare Function GetLastError Lib "kernel32" () As Long
'
' Retrieves the results of an overlapped operation on the
' specified file, named pipe, or communications device.
'
Private Declare Function GetOverlappedResult Lib "kernel32" _
(ByVal hFile As Long, lpOverlapped As OVERLAPPED, _
lpNumberOfBytesTransferred As Long, ByVal bWait As Long) As Long
'
' Discards all characters from the output or input buffer of a
' specified communications resource. It can also terminate
' pending read or write operations on the resource.
'
Private Declare Function PurgeComm Lib "kernel32" _
(ByVal hFile As Long, ByVal dwFlags As Long) As Long
'
' Reads data from a file, starting at the position indicated by the
' file pointer. After the read operation has been completed, the
' file pointer is adjusted by the number of bytes actually read,
' unless the file handle is created with the overlapped attribute.
' If the file handle is created for overlapped input and output
' (I/O), the application must adjust the position of the file pointer
' after the read operation.
'
Private Declare Function ReadFile Lib "kernel32" _
(ByVal hFile As Long, ByVal lpBuffer As String, _
ByVal nNumberOfBytesToRead As Long, ByRef lpNumberOfBytesRead As Long, _
lpOverlapped As OVERLAPPED) As Long
'
' Configures a communications device according to the specifications
' in a device-control block (a DCB structure). The function
' reinitializes all hardware and control settings, but it does not
' empty output or input queues.
'
Private Declare Function SetCommState Lib "kernel32" _
(ByVal hCommDev As Long, lpDCB As DCB) As Long
'
' Sets the time-out parameters for all read and write operations on a
' specified communications device.
'
Private Declare Function SetCommTimeouts Lib "kernel32" _
(ByVal hFile As Long, lpCommTimeouts As COMMTIMEOUTS) As Long
'
' Initializes the communications parameters for a specified
' communications device.
'
Private Declare Function SetupComm Lib "kernel32" _
(ByVal hFile As Long, ByVal dwInQueue As Long, ByVal dwOutQueue As Long) As Long
'
' Writes data to a file and is designed for both synchronous and a
' synchronous operation. The function starts writing data to the file
' at the position indicated by the file pointer. After the write
' operation has been completed, the file pointer is adjusted by the
' number of bytes actually written, except when the file is opened with
' FILE_FLAG_OVERLAPPED. If the file handle was created for overlapped
' input and output (I/O), the application must adjust the position of
' the file pointer after the write operation is finished.
'
Private Declare Function WriteFile Lib "kernel32" _
(ByVal hFile As Long, ByVal lpBuffer As String, _
ByVal nNumberOfBytesToWrite As Long, lpNumberOfBytesWritten As Long, _
lpOverlapped As OVERLAPPED) As Long

Private Declare Sub AppSleep Lib "kernel32" Alias "Sleep" (ByVal dwMilliseconds
As Long)
'-------------------------------------------------------------------------------
' Program Constants
'-------------------------------------------------------------------------------

Private Const MAX_PORTS = 4

'-------------------------------------------------------------------------------
' Program Structures
'-------------------------------------------------------------------------------

Private Type COMM_ERROR
lngErrorCode As Long
strFunction As String
strErrorMessage As String
End Type

Private Type COMM_PORT
lngHandle As Long
blnPortOpen As Boolean
udtDCB As DCB
End Type

'-------------------------------------------------------------------------------
' Program Storage
'-------------------------------------------------------------------------------

Private udtCommOverlap As OVERLAPPED
Private udtCommError As COMM_ERROR
Private udtPorts(1 To MAX_PORTS) As COMM_PORT
'-------------------------------------------------------------------------------
' GetSystemMessage - Gets system error text for the specified error code.
'-------------------------------------------------------------------------------
Public Function GetSystemMessage(lngErrorCode As Long) As String
Dim intPos As Integer
Dim strMessage As String, strMsgBuff As String * 256

Call FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, 0, lngErrorCode, 0, strMsgBuff,
255, 0)

intPos = InStr(1, strMsgBuff, vbNullChar)
If intPos > 0 Then
strMessage = Trim$(Left$(strMsgBuff, intPos - 1))
Else
strMessage = Trim$(strMsgBuff)
End If

GetSystemMessage = strMessage

End Function
Public Function PauseApp(PauseInSeconds As Long)

Call AppSleep(PauseInSeconds * 1000)

End Function

'-------------------------------------------------------------------------------
' CommOpen - Opens/Initializes serial port.
'
'
' Parameters:
' intPortID - Port ID used when port was opened.
' strPort - COM port name. (COM1, COM2, COM3, COM4)
' strSettings - Communication settings.
' Example: "baud=9600 parity=N data=8 stop=1"
'
' Returns:
' Error Code - 0 = No Error.
'
'-------------------------------------------------------------------------------
Public Function CommOpen(intPortID As Integer, strPort As String, _
strSettings As String) As Long

Dim lngStatus As Long
Dim udtCommTimeOuts As COMMTIMEOUTS

On Error GoTo Routine_Error

' See if port already in use.
If udtPorts(intPortID).blnPortOpen Then
lngStatus = -1
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommOpen"
.strErrorMessage = "Port in use."
End With

GoTo Routine_Exit
End If

' Open serial port.
udtPorts(intPortID).lngHandle = CreateFile(strPort, GENERIC_READ Or _
GENERIC_WRITE, 0, ByVal 0&, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)

If udtPorts(intPortID).lngHandle = -1 Then
lngStatus = SetCommError("CommOpen (CreateFile)")
GoTo Routine_Exit
End If

udtPorts(intPortID).blnPortOpen = True

' Setup device buffers (1K each).
lngStatus = SetupComm(udtPorts(intPortID).lngHandle, 1024, 1024)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (SetupComm)")
GoTo Routine_Exit
End If

' Purge buffers.
lngStatus = PurgeComm(udtPorts(intPortID).lngHandle, PURGE_TXABORT Or _
PURGE_RXABORT Or PURGE_TXCLEAR Or PURGE_RXCLEAR)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (PurgeComm)")
GoTo Routine_Exit
End If

' Set serial port timeouts.
With udtCommTimeOuts
.ReadIntervalTimeout = -1
.ReadTotalTimeoutMultiplier = 0
.ReadTotalTimeoutConstant = 1000
.WriteTotalTimeoutMultiplier = 0
.WriteTotalTimeoutConstant = 1000
End With

lngStatus = SetCommTimeouts(udtPorts(intPortID).lngHandle, udtCommTimeOuts)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (SetCommTimeouts)")
GoTo Routine_Exit
End If

' Get the current state (DCB).
lngStatus = GetCommState(udtPorts(intPortID).lngHandle, _
udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (GetCommState)")
GoTo Routine_Exit
End If

' Modify the DCB to reflect the desired settings.
lngStatus = BuildCommDCB(strSettings, udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (BuildCommDCB)")
GoTo Routine_Exit
End If

' Set the new state.
lngStatus = SetCommState(udtPorts(intPortID).lngHandle, _
udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommOpen (SetCommState)")
GoTo Routine_Exit
End If

lngStatus = 0

Routine_Exit:
CommOpen = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommOpen"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

Private Function SetCommError(strFunction As String) As Long

With udtCommError
.lngErrorCode = Err.LastDllError
.strFunction = strFunction
.strErrorMessage = GetSystemMessage(.lngErrorCode)
SetCommError = .lngErrorCode
End With

End Function

Private Function SetCommErrorEx(strFunction As String, lngHnd As Long) As Long
Dim lngErrorFlags As Long
Dim udtCommStat As COMSTAT

With udtCommError
.lngErrorCode = GetLastError
.strFunction = strFunction
.strErrorMessage = GetSystemMessage(.lngErrorCode)

Call ClearCommError(lngHnd, lngErrorFlags, udtCommStat)

.strErrorMessage = .strErrorMessage & " COMM Error Flags = " & _
Hex$(lngErrorFlags)

SetCommErrorEx = .lngErrorCode
End With

End Function

'-------------------------------------------------------------------------------
' CommSet - Modifies the serial port settings.
'
' Parameters:
' intPortID - Port ID used when port was opened.
' strSettings - Communication settings.
' Example: "baud=9600 parity=N data=8 stop=1"
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommSet(intPortID As Integer, strSettings As String) As Long

Dim lngStatus As Long

On Error GoTo Routine_Error

lngStatus = GetCommState(udtPorts(intPortID).lngHandle, _
udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommSet (GetCommState)")
GoTo Routine_Exit
End If

lngStatus = BuildCommDCB(strSettings, udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommSet (BuildCommDCB)")
GoTo Routine_Exit
End If

lngStatus = SetCommState(udtPorts(intPortID).lngHandle, _
udtPorts(intPortID).udtDCB)

If lngStatus = 0 Then
lngStatus = SetCommError("CommSet (SetCommState)")
GoTo Routine_Exit
End If

lngStatus = 0

Routine_Exit:
CommSet = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommSet"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' CommClose - Close the serial port.
'
' Parameters:
' intPortID - Port ID used when port was opened.
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommClose(intPortID As Integer) As Long

Dim lngStatus As Long

On Error GoTo Routine_Error

If udtPorts(intPortID).blnPortOpen Then
lngStatus = CloseHandle(udtPorts(intPortID).lngHandle)

If lngStatus = 0 Then
lngStatus = SetCommError("CommClose (CloseHandle)")
GoTo Routine_Exit
End If

udtPorts(intPortID).blnPortOpen = False
End If

lngStatus = 0

Routine_Exit:
CommClose = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommClose"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' CommFlush - Flush the send and receive serial port buffers.
'
' Parameters:
' intPortID - Port ID used when port was opened.
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommFlush(intPortID As Integer) As Long

Dim lngStatus As Long

On Error GoTo Routine_Error

lngStatus = PurgeComm(udtPorts(intPortID).lngHandle, PURGE_TXABORT Or _
PURGE_RXABORT Or PURGE_TXCLEAR Or PURGE_RXCLEAR)

If lngStatus = 0 Then
lngStatus = SetCommError("CommFlush (PurgeComm)")
GoTo Routine_Exit
End If

lngStatus = 0

Routine_Exit:
CommFlush = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommFlush"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' 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 * 1024
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
'------------------------------------------------------------------------------------

lngRdSize = lngSize
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

'-------------------------------------------------------------------------------
' CommWrite - Output data to the serial port.
'
' Parameters:
' intPortID - Port ID used when port was opened.
' strData - Data to be transmitted.
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommWrite(intPortID As Integer, strData As String) As Long

Dim i As Integer
Dim lngStatus As Long, lngSize As Long
Dim lngWrSize As Long, lngWrStatus As Long

On Error GoTo Routine_Error

' Get the length of the data.
lngSize = Len(strData)

' Output the data.
lngWrStatus = WriteFile(udtPorts(intPortID).lngHandle, strData, lngSize, _
lngWrSize, udtCommOverlap)

' Note that normally the following code will not execute because the driver
' caches write operations. Small I/O requests (up to several thousand bytes)
' will normally be accepted immediately and WriteFile will return true even
' though an overlapped operation was specified.

DoEvents

If lngWrStatus = 0 Then
lngStatus = GetLastError
If lngStatus = 0 Then
GoTo Routine_Exit
ElseIf lngStatus = ERROR_IO_PENDING Then
' We should wait for the completion of the write operation so we know
' if it worked or not.
'
' This is only one way to do this. It might be beneficial to place the
' writing operation in a separate thread so that blocking on completion
' will not negatively affect the responsiveness of the UI.
'
' If the write takes long enough to complete, this function will
' timeout
' according to the CommTimeOuts.WriteTotalTimeoutConstant variable.
' At that time we can check for errors and then wait some more.

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

lngStatus = GetLastError

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

lngStatus = SetCommErrorEx("CommWrite (WriteFile)", _
udtPorts(intPortID).lngHandle)
GoTo Routine_Exit

End If
End If

For i = 1 To 10
DoEvents
Next

Routine_Exit:
CommWrite = lngWrSize
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommWrite"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' CommGetLine - Get the state of selected serial port control lines.
'
' Parameters:
' intPortID - Port ID used when port was opened.
' intLine - Serial port line. CTS, DSR, RING, RLSD (CD)
' blnState - Returns state of line (Cleared or Set).
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommGetLine(intPortID As Integer, intLine As Integer, _
blnState As Boolean) As Long

Dim lngStatus As Long
Dim lngComStatus As Long, lngModemStatus As Long

On Error GoTo Routine_Error

lngStatus = GetCommModemStatus(udtPorts(intPortID).lngHandle, lngModemStatus)

If lngStatus = 0 Then
lngStatus = SetCommError("CommReadCD (GetCommModemStatus)")
GoTo Routine_Exit
End If

If (lngModemStatus And intLine) Then
blnState = True
Else
blnState = False
End If

lngStatus = 0

Routine_Exit:
CommGetLine = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommReadCD"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' CommSetLine - Set the state of selected serial port control lines.
'
' Parameters:
' intPortID - Port ID used when port was opened.
' intLine - Serial port line. BREAK, DTR, RTS
' Note: BREAK actually sets or clears a "break" condition on
' the transmit data line.
' blnState - Sets the state of line (Cleared or Set).
'
' Returns:
' Error Code - 0 = No Error.
'-------------------------------------------------------------------------------
Public Function CommSetLine(intPortID As Integer, intLine As Integer, _
blnState As Boolean) As Long

Dim lngStatus As Long
Dim lngNewState As Long

On Error GoTo Routine_Error

If intLine = LINE_BREAK Then
If blnState Then
lngNewState = SETBREAK
Else
lngNewState = CLRBREAK
End If

ElseIf intLine = LINE_DTR Then
If blnState Then
lngNewState = SETDTR
Else
lngNewState = CLRDTR
End If

ElseIf intLine = LINE_RTS Then
If blnState Then
lngNewState = SETRTS
Else
lngNewState = CLRRTS
End If
End If

lngStatus = EscapeCommFunction(udtPorts(intPortID).lngHandle, lngNewState)

If lngStatus = 0 Then
lngStatus = SetCommError("CommSetLine (EscapeCommFunction)")
GoTo Routine_Exit
End If

lngStatus = 0

Routine_Exit:
CommSetLine = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
.lngErrorCode = lngStatus
.strFunction = "CommSetLine"
.strErrorMessage = Err.Description
End With
Resume Routine_Exit
End Function

'-------------------------------------------------------------------------------
' CommGetError - Get the last serial port error message.
'
' Parameters:
' strMessage - Error message from last serial port error.
'
' Returns:
' Error Code - Last serial port error code.
'-------------------------------------------------------------------------------
Public Function CommGetError(strMessage As String) As Long

With udtCommError
CommGetError = .lngErrorCode
strMessage = "Error (" & CStr(.lngErrorCode) & "): " & .strFunction & _
" - " & .strErrorMessage
End With

End Function



Private Sub CommandButton1_Click()
Dim intPortID As Integer ' Ex. 1, 2, 3, 4 for COM1 - COM4
Dim lngStatus As Long

intPortID = 1

' Open COM port
lngStatus = CommOpen(intPortID, "COM" & CStr(intPortID), _
"baud=9600 parity=N data=8 stop=1")
End Sub



Private Sub CommandButton2_Click()

Dim intPortID As Integer ' Ex. 1, 2, 3, 4 for COM1 - COM4
Dim lngStatus As Long
Dim strData As String

intPortID = 1
strData = "*IDN?;"

'Writa data
lngStatus = CommWrite(intPortID, strData)

End Sub



Private Sub CommandButton3_Click()

Dim intPortID As Integer ' Ex. 1, 2, 3, 4 for COM1 - COM4
Dim lngStatus As Long
Dim strData As String

intPortID = 1
lngStatus = CommRead(intPortID, strData, 10)

End Sub



Private Sub CommandButton4_Click()

Dim intPortID As Integer ' Ex. 1, 2, 3, 4 for COM1 - COM4

intPortID = 1
Call CommClose(intPortID)

End Sub

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