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VB Forum / General 2 / November 2005Passing a VB MSComm Control Object as a parameter
I have a VB 6 application that uses the MSComm control to communicate with a BootStrap Loader on a TI Chip. I would like to create a DLL so that other applications can call the BootStrap functions. I have created an ActiveX DLL and in order to test that this will work, I wanted to implement just one of the functions in the ActiveX DLL and prove it out. The function I chose is startBSL, which sets/clears the DTR and RTS signals to tell the TI Chip to go into BootStrap mode. I moved the function into the ActiveX DLL as a method in the BSL class. I call the method from the original VB 6 application and pass the MSComm control to the DLL. ActiveX DLL contains class BSL_Class with the following method: Public Function startBSL (ByVal pc_comm as Object) as Boolean VB 6 application contains an MSComm control names MSComm1 and the following code: Public BSLDLL as BSL_Class Set BSLDLL = New BSL_Class Ack = BSLDLL.startBSL(MSComm1) The ActiveX DLL and the application build without errors, but when I run the application, I get the following error on the BSLDLL.startBSL line run-time error '424' object required I saw some postings that indicated I should be able to do this, but I am running out of ideas. Help would be greatly appreciated, Stacy >I have a VB 6 application that uses the MSComm control to communicate >with a BootStrap Loader on a TI Chip. I would like to create a DLL so [quoted text clipped - 24 lines] > >run-time error '424' object required I think I understand what you are up to The MSCOM.CommID Property contains the Windows File Handle of an open Comm port - one can use the APIs to toggle CTS and DTR - it might be simpler ... BTW I don't think you should pass an Object ByVal Thanks for the help, I've read alot of posts about how to pass an object, opinions differ. If you don't mind another question, What API's can I use to toggle CTS and DTR? I find that the Windows documentation makes finding the correct API very difficult if you don't know it's name. Stacy >Thanks for the help, I've read alot of posts about how to pass an >object, opinions differ. If you don't mind another question, What >API's can I use to toggle CTS and DTR? I find that the Windows >documentation makes finding the correct API very difficult if you don't >know it's name. True - it requires digging through the Win32 Programmer's Help File Do you have that ? If not : www.jerryfrench.co.uk/utils/win32sdk.zip (it is old but very useful) Here are some snippets from my COMM opus :- Private Declare Function EscapeCommFunction Lib "kernel32" ( _ ByVal nCid As Long, _ ByVal nFunc As Long) As Long Private Declare Function GetCommModemStatus Lib "kernel32" ( _ ByVal hFile As Long, _ lpModemStat As Long) As Long 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 CLRDTR = 6 ' Clears the DTR (data-terminal-ready) signal. Private Const CLRRTS = 4 ' Clears the RTS (request-to-send) signal. Private Const SETDTR = 5 ' Sends the DTR (data-terminal-ready) signal. Private Const SETRTS = 3 ' Sends the RTS (request-to-send) signal. Public Sub DtrOn(Erm$) Erm$ = "" If EscapeCommFunction(cmn.hFile, SETDTR) = 0 Then Erm$ = "Failed EscapeCommFunction() SETDTR" End If End Sub Public Sub DtrOff(Erm$) Erm$ = "" If EscapeCommFunction(cmn.hFile, CLRDTR) = 0 Then Erm$ = "Failed EscapeCommFunction() CLRDTR" End If End Sub ........ If GetCommModemStatus(cmn.hFile, Status) = 0 Then Erm$ = "Failed GetCommModemStatus" Exit Function End If ' --- If Status And MS_CTS_ON Then LF_CTS_On = True Exit Function End If >BTW I don't think you should pass an Object ByVal I always pass object references ByVal, unless the object is a "return" or "out" parameter. Remember that ByVal does not copy or clone the object, it just makes a 4 byte copy of the object reference (or pointer). In fact, I use ByVal on all datatypes except extremely large Strings (and of course arrays and user-defined types). My two cents, Tom >>BTW I don't think you should pass an Object ByVal > [quoted text clipped - 3 lines] >Remember that ByVal does not copy or clone the object, it just makes a >4 byte copy of the object reference (or pointer). Yes, I stand corrected I suspect that creating another reference will bump up the reference count, but that is no hardship > The ActiveX DLL and the application build without errors, but when I > run the application, I get the following error on the BSLDLL.startBSL > line > > run-time error '424' object required Unless you are debugging with the source code of the DLL, the error occurring on the BSLDLL.startBSL line may mean only that an error occurred somewhere in the DLL. Also, Jerry's note about not passing an object by value may be more relevant for a control such as MSComm, since a control has to be on a form and be loaded, etc., so it can't be passed by value as easily. |
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