Re: Serial communication - C / C++ / MFC Discussion Boards

Re: Serial communication

CPallini14-Apr-08 4:04

CPallini

14-Apr-08 4:04

Did you check all return values?
CreateFile returns a valid handle?
GetCommState and SetCommState return TRUE?

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

Re: Serial communication

FPeeters14-Apr-08 4:36

FPeeters

14-Apr-08 4:36

As far as I can tell CreateFile returns a valid Handle and GetCommState and SetCommState are true.
Here is in pseudo-code how I did it:

hComm=CreateFile(("COM1"), GENERIC_READ|GERERIC_WRITE,0,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0);
if (hComm == INVALID_HANDLE_VALUE)
//ERROR MESSAGE TO LISTBOX
else
//OK MESSAGE TO LISTBOX
if (!GetCommState(hComm,&dcb))
//ERROR MESSAGE TO LISTBOX
else
//OK MESSAGE TO LISTBOX
if (!SetCommState(hComm, &dcb))
//ERROR MESSAGE TO LISTBOX
else
//OK MESSAGE TO LISTBOX
if(osReader.hEvent == NULL)
//ERROR MESSAGE TOLISTBOX
else
while (ReadActive)
if(!ReadFile(hComm,lpBuff,sizeof(lpBuff),&dwRead,&osReader))
//ERROR MESSAGE TO LISTBOX
else
dwResult = WaitForSingleObject(osReader.hEvent, READ_TIMEOUT);
switch(dwResult)
case WAIT_OBJECT_0
case WAIT_TIMEOUT
default

So if I get an INVALID_HANDLE_VALUE the rest of the code is skipped and an errormessage is written in a ListBox, also if either the GetCommState() and SetCommState() function restuns FALSE I should receive an error message in this ListBox. But I don't receive an error message and the app reports a Time-out on the Listbox.

Re: Serial communication

CPallini14-Apr-08 5:45

CPallini

14-Apr-08 5:45

Maybe the read operation was completed before the wait starts. Why don't you call GetOverlappedResult?

Re: Serial communication

Randor 14-Apr-08 6:28

Randor

14-Apr-08 6:28

My question is:

Why is he opening a bar code scanner with FILE_FLAG_OVERLAPPED in the first place. I have never seen a bar code scanner which required overlapped I/O.

Best Wishes,
David Delaune

Re: Serial communication

CPallini14-Apr-08 6:48

CPallini

14-Apr-08 6:48

Maybe his application requires it.
Smile | :)

Re: Serial communication

FPeeters14-Apr-08 20:56

FPeeters

14-Apr-08 20:56

No the reason why I used this kind of IO is quit simple: I couldn't find any explanation on how to run the COM port otherwise... So if there is any suggestion on how to work with a barcode scanner I would like to know.

Re: Serial communication

CPallini14-Apr-08 22:11

CPallini

14-Apr-08 22:11

You can simply use COM synchronously.
Smile | :)

Re: Serial communication

FPeeters14-Apr-08 22:24

FPeeters

14-Apr-08 22:24

In all the articles I've found everyone says you can use com synchronously but no-one explains it.
I am a starter on C++ (formerly programming PLC's and slowly changing over to PC control for some machines).

OMG | :OMG:

Re: Serial communication

CPallini14-Apr-08 22:47

CPallini

14-Apr-08 22:47

If you configure a COM for synchronous operations (see for instance [^]) then each call to ReadFile becomes a blocking one (until timeout expires, see [^]).
Smile | :)

Re: Serial communication

FPeeters14-Apr-08 23:09

FPeeters

14-Apr-08 23:09

Thanks for the info, but to go back to my original problem: Does this solve it, or is it a better way to communicate for me with the com port?

Re: Serial communication

CPallini14-Apr-08 23:23

CPallini

14-Apr-08 23:23

At least, you can try.
Smile | :)

Re: Serial communication

FPeeters14-Apr-08 23:25

FPeeters

14-Apr-08 23:25

OK I deserved that one, ofcourse I can try, and I will..
Big Grin | :-D

Re: Serial communication

FPeeters15-Apr-08 2:40

FPeeters

15-Apr-08 2:40

Okay, I've tried the synchrounous approach but there is no change in the situation.

Re: Serial communication

David Crow14-Apr-08 5:19

David Crow

14-Apr-08 5:19

FPeeters wrote:
I configure a connection between my app and the COM1 port of a PC using the following piece of code:

hComm = CreateFile(("COM1"),

Shouldn't this be:

CreateFile("\\\\.\\COM1", ...);

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: Serial communication

Randor 14-Apr-08 5:27

Randor

14-Apr-08 5:27

Both methods are correct. You could consider "COM1" as a mapping to "\\\\.\\COM1" such as is created by DefineDosDevice[^]

Best Wishes,
-David Delaune

Re: Serial communication

FPeeters14-Apr-08 5:35

FPeeters

14-Apr-08 5:35

DavidCrow wrote:
Shouldn't this be:

CreateFile("\\\\.\\COM1", ...);

This is, sadly enough, not the solution to my problem. But I'm curious: what is the meaning of "\\\\.\\"

Re: Serial communication

David Crow14-Apr-08 5:50

David Crow

14-Apr-08 5:50

FPeeters wrote:
But I'm curious: what is the meaning of "\\\\.\\"

It's just a format that some arguments to CreateFile() must have. COM1 must not be one of those. Sorry 'bout that.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: Serial communication

CPallini14-Apr-08 6:53

CPallini

14-Apr-08 6:53

It is the UNC [^] path of COM1.

Re: Serial communication

Randor 14-Apr-08 5:35

Randor

14-Apr-08 5:35

Hello Frank,

You should paste the contents of your DCB structure so I can take a look at it. There are some combinations of values that do not work. If you are also setting the COMMTIMEOUTS structure please paste that here as well.

Best Wishes,
-David Delaune

Re: Serial communication

FPeeters14-Apr-08 21:20

FPeeters

14-Apr-08 21:20

DCB structure:
DCBLength = 28
BaudRate = 38400
fBinary = 1
fParity = 0
fOutxCtsFlow = 0
fOutxDsrFlow = 0
fDtrControl = 1
fDsrSensitivity = 0
fTXContinueOnXoff = 1
fOutX = 0
fInX = 0
fErrorChar = 0
fNull = 0
fRtsControl = 1
fAbortOnError =1
fDummy2 = 0 (this one is not used but added for the complete structure)
wReserved = 0 (this one is not used but added for the complete structure)
XonLim = 2048
XoffLim = 512
ByteSize = 7
Parity = 0
StopBits = 0
XonChar = 17
XoffChar = 19
ErrorChar = 0
EvtChar = 0
wReserved1 = 0 (this one is not used but added for the complete structure)

The current settings for the Barcode reader are:
BaudRate = 38400 (default value)
DataBits = 7
Parity = NONE
StopBits = 1
RTS/CTS HardwareFlowcontrol = Off
Xon/Xoff SoftWareFlowControl = Off
Ack/Nak SoftwareFlowControl = Off

As for the COMMTIMEOUTS structure: I don't know if I am using this structure. I defined a constant (#define READ_TIMEOUT 5000) and use that in "WaitForSingleObject"

I hope you can send my in the right direction on solving this problem. Please explain any recommended changes in these settings so I can learn from it and avoid this in the future.

Re: Serial communication

Randor 16-Apr-08 9:44

Randor

16-Apr-08 9:44

Sorry for the delay, I was not in the office yesterday.

You have some things wrong in your DCB structure.

FPeeters wrote:
The current settings for the Barcode reader are:

HardwareFlowcontrol should be off according to your statement on the bottom.

You should make the following changes:

if(TRUE == GetCommState(m_hComm, &m_dcb))
{
	m_dcb.BaudRate = CBR_38400;
	m_dcb.Parity = NOPARITY;
	m_dcb.StopBits = ONESTOPBIT;
	m_dcb.fDtrControl = DTR_CONTROL_DISABLE;
	m_dcb.fRtsControl = RTS_CONTROL_DISABLE;
	m_dcb.fOutxCtsFlow = FALSE;
	m_dcb.fOutxDsrFlow = FALSE;
	m_dcb.fOutX = FALSE;
	m_dcb.fInX = FALSE;
	m_dcb.ByteSize = 7;
	if(FALSE == SetCommState(m_hComm, &m_dcb))
	{
		TRACE0(_T("FAILED.\n"));
	}
}

I am almost positive that you should change FILE_FLAG_OVERLAPPED to NULL when you open the COM port. I highly doubt that you need to do overlapped I/O with a barcode reader. Don't worry about the COMMTIMEOUTS for now, I was asking this question with the assumption that you were possibly performing overlapped i/o and the timeout structure would effect this.

Here is a good MSDN containing the explanation for the DCB fields. It looks like you just need to match what the barcode scanner is expecting.

http://msdn2.microsoft.com/en-us/library/aa363214(VS.85).aspx[^]

Best Wishes,
-David Delaune

Re: Serial communication

FPeeters16-Apr-08 22:23

FPeeters

16-Apr-08 22:23

No problem with the delay, by opening and closing the connection with hyperterminal I can solve the problem for a while (until I shutdown or reboot my computer) so it not stopping me in the development of the app.

I've tested our proposed settings of the DCB structure, but unfortunatly it doesn't solve the problem.

if (!GetCommState(hComm, &dcb))<br />
{<br />
	sprintf(str,"GET_COMM_STATE FAILED");<br />
	::MessageBox(0,str,"FOUT",MB_OK);<br />
}<br />
else<br />
{<br />
	//port config<br />
	dcb.BaudRate = CBR_38400;<br />
	dcb.Parity = NOPARITY;<br />
	dcb.StopBits = ONESTOPBIT;<br />
	dcb.fDtrControl = DTR_CONTROL_DISABLE;<br />
	dcb.fRtsControl = RTS_CONTROL_DISABLE;<br />
	dcb.fOutxCtsFlow = false;<br />
	dcb.fOutxDsrFlow = false;<br />
	dcb.fOutX = false;<br />
	dcb.fInX = false;<br />
	dcb.ByteSize = 7;<br />
<br />
	if (!SetCommState(hComm, &dcb))<br />
	{<br />
		//send message to ListBox<br />
		sprintf(str,"SETCOMMSTATE ERROR");<br />
		::MessageBox(0,str,"FOUT",MB_OK);<br />
	}<br />
	else<br />
	{<br />
		//send message to ListBox<br />
        }

I've found the suggested MSDN already, but thanks for the suggestion.

Is there a possibility to check the settings of the HyperTerminal programm in a DCB-structure, so I can see what settings this programm uses and copy them?
Or when I start Hyperterminal and close it again and then use the GetCommState command, do I get the settings Hyperterminal used?
Maybe HyperTerminal sends some activating code to any connected device?

Frank Peeters.

Application Instance

john563214-Apr-08 1:36

john5632

14-Apr-08 1:36

Hi,

I have a application that allow to run multiple instances. If at same time two instances are runnining and I want to close one with another exe throgh ProcessTreminate() command then how can I differentiate these two instances which is to be close.

Re: Application Instance

Rajesh R Subramanian14-Apr-08 1:51

Rajesh R Subramanian

14-Apr-08 1:51

pther wrote:
If at same time two instances are runnining and I want to close one with another exe throgh ProcessTreminate() command

Why don't you instead restrict the number of instances of your application to just one?

Here's a reference link: Avoiding multiple instances[^]

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: Application Instance

Rajkumar R14-Apr-08 2:01

Rajkumar R

14-Apr-08 2:01

pther wrote:
how can I differentiate these two instances

you may need to enumerate the processes(EnumProcesses) and find whether the process is created by same executable file (GetModuleBaseName) and the process ID differentiates the multiple instance.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.