Re : Trouble connecting a line in Change Detection Interrupt mode and read staticly value: CVI 9, DaqMx and board PCI32HS

[damien.]

Hi everybody,

For my application, I have to do a job in case of change on a line, by interrupt, but i have also to read (static mode) the status of these line, on demand...

What is wrong in my code ?

My initalisation is done like this :

DAQmxCreateTask("Task",&TaskHandle)
DAQmxCreateDIChan (TaskHandle, "/dev1/port0", "", DAQmx_Val_ChanForAllLines); 
DAQmxCfgChangeDetectionTiming (TaskHandle, "/dev1/port0"," /dev1/port0", DAQmx_Val_ContSamps, 1);
DAQmxRegisterSignalEvent (TaskHandle, DAQmx_Val_ChangeDetectionEvent, 0, ChangeDetectedCallBack, NULL);
DAQmxStartTask (TaskHandle);


The interrupt function fire successfully in case of change... Correct line value is read... no problem here

The problem is, for my application, i have also to read, from another part of my software, completely asynchronously, the value for these line :


To do it, i use something like that :
uInt8    Data = 0;
DAQmxReadDigitalU8 (TaskHandle, DAQmx_Val_Auto, 10.0, DAQmx_Val_GroupByChannel, &Data, 1,&NbElementRead, 0); 


Now, inside the interrupt callback function, i read the correct value, (fairly logical because the change event was the condition to trig a sample)...
But from another piece of code, I will ask for a reading but change hasn't occured and reading not trigged. Then, i will read always 0 (i'm surprised to don't receive an error such: Buffer empty... anyway...)

How i could manage to fix this trouble ?


Tanks in advance

Damien
 

[Rémi M]

Hello Damien,

The ReadDigitalU8 function expects an array to get the points, otherwise you can use the ReadDigitalScalar if you want to get only one value.

The DAQmx ReadDigital for the change detection task waits for change to occur to fetch the points. If you want to simply read the port, you would need another task creation. However, you cannot have both Change detection and on demand DI read tasks on the same port at the same time.

Regarding your application, you might consider writing the result of your change detection task's reading in a variable so as to read it from another program. Since the change detection gives you the value of the port the last time there was a change on it, reading the port should give the same values as reading the last change detection acquisition.

I hope this help

Have a nice day,

[Nguyen.Hung]

Hi

I have Same trouble.

My code here.

int32 CVICALLBACK DIChangeDetection(TaskHandle taskHandle, int32 signalID, void *callbackData)
{
	int32	error = 0, nSample = 0, numRead = 0, i;
	if(!_hTaskNI_DAQ_DI)
		return 0;
	DAQmxErrChk (DAQmxReadDigitalLines(_hTaskNI_DAQ_DI,1,2.0,DAQmx_Val_GroupByScanNumber,_dataDIChannels,32,&numRead,NULL,NULL));

Error:
	return 0;
}
In Main
{
......
(devName = DEV1)

sprintf(buf,"%s/port0/line2:11",devName);
	DAQmxErrChk (DAQmxCreateTask("",&_hTaskNI_DAQ_DI));
	DAQmxErrChk (DAQmxCreateDIChan(_hTaskNI_DAQ_DI,buf,"",DAQmx_Val_ChanPerLine));
	DAQmxErrChk (DAQmxCfgChangeDetectionTiming(_hTaskNI_DAQ_DI, buf, buf,DAQmx_Val_ContSamps,1));
	DAQmxErrChk (DAQmxRegisterSignalEvent(_hTaskNI_DAQ_DI,DAQmx_Val_ChangeDetectionEvent,0,DIChangeDetection,NULL));

...
}

 DI changeDetection was fired but when I connect 10 signal to line 2:11 in the same time. DI Change detection event didn't fire after about 60000 time ( once signal occur mycounter += 1;). Can U show me what happend. (I think it seem do not regconize the raising or falling edge after amount of event. Other task in my Application is still ok as reading ai channel)

I Use DAQ M series 6259. Frequence of signal is 100Hz.