Externally triggered continuous acquisition (ANSI C)

[PeVa]

Almighty gurus,

I'm total beginner in the NI-world, so sorry if I'm forgetting something obvious.

my environment: USB-9423, WinXP SP3, MS Visual Studio 2008

My problem is fairly simple: at raising edge of line0 I want to read status of line1. I copied the ANSI-C example "ContReadDigChan-ExtClk.c" and tried to modify parameters to achieve my goal. I'm not able to force my program to read just one sample at the raising-edge of line0, apparently I'm receiving intermittent numbers of samples. What I'm doing wrong? Many thanks for any helpful hints... 

Petr

Here is my main()

int main(int argc, char *argv)
{

	int32		error=0;
	TaskHandle	taskHandle=0;
	uInt8		data[1];
	int32		sampsRead,totalRead=0;
	char		errBuff[2048]={'\0'};

	/*********************************************/
	// DAQmx Configure Code
	/*********************************************/
	DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
	DAQmxErrChk (DAQmxCreateDIChan(taskHandle,"CDAQ1Mod1/port0/line1","",DAQmx_Val_ChanPerLine));
	DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"/CDAQ1Mod1/PFI0",1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1));

	/*********************************************/
	// DAQmx Start Code
	/*********************************************/
	DAQmxErrChk (DAQmxStartTask(taskHandle));

	printf("Acquiring samples continuously. Press Ctrl+C to interrupt\n");
	while( 1 ) {
		/*********************************************/
		// DAQmx Read Code
		/*********************************************/
		DAQmxErrChk (DAQmxReadDigitalU8(taskHandle,1,10.0,DAQmx_Val_GroupByChannel,data,1,&sampsRead,NULL));

		if( sampsRead>0 ) {
			totalRead++;;
			printf("Acquired %d samples (%i)\n", totalRead, data[0]);
			fflush(stdout);
		}
	}

Error:
	if( DAQmxFailed(error) )
		DAQmxGetExtendedErrorInfo(errBuff,2048);
	if( taskHandle!=0 ) {
		/*********************************************/
		// DAQmx Stop Code
		/*********************************************/
		DAQmxStopTask(taskHandle);
		DAQmxClearTask(taskHandle);
	}
	if( DAQmxFailed(error) )
		printf("DAQmx Error: %s\n",errBuff);
	return 0;

}