Dear Samantha,
Thank you so much. The following is the whole thing. Maybe the reason of the problem is that I am using NI_DAQmx Base , not NI_DAQmx. Thanks.
I started from the example and did some modifications. First I met -200284 error and I found it is the caused by wrong number of data to be read. I changed to finite namber data read.
Then I met sixth reading problem, at that time I use a button clicking to read the data.when I read for the sixth time, It will occur (I forgot the phenomena). I added a
stop task function and I thought I solved the problem. I knew for a finite number data reading, stop function is not needed, but I do not have any other method so I tried it. "sixth reading problem" solved, but When I move the data reading function to ontimer function recently. The program will halt -- take 99% of CPU time after 30 second of reading (sometime several minutes, sometimes several seconds). If I move the start task back to OnInitialUpdate() function and cancel stop function, halt error will not occur but the data I read in not correct. That is the whole thing. The following is the code relative to the data read.
Initialization;
void Ctest2Dlg:nInitialUpdate()
{.....
DAQmxErrChk (DAQmxBaseCreateTask("",&taskHandle));
DAQmxErrChk (DAQmxBaseCreateAIVoltageChan(taskHandle,chan,"",DAQmx_Val_RSE,min,max,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxBaseCfgSampClkTiming(taskHandle,clockSource,sampleRate,DAQmx_Val_Rising,DAQmx_Val_ContSamps ,samplesPerChan));
.....
}
Data read
void Ctest2Dlg:nTimer(UINT nIDEvent)
{
.....
if(taskHandle != 0)
{
DAQmxErrChk (DAQmxBaseStartTask(taskHandle));
DAQmxErrChk (DAQmxBaseReadAnalogF64(taskHandle,pointsToRead,timeout,DAQmx_Val_GroupByScanNumber,data,100,&pointsRead,NULL));
DAQmxBaseStopTask (taskHandle);
}
.....
}
Definition of parameter:
#include "NIDAQmxBase.h"
//////////////////////////////////////////////////
// Task parameters
int TaskOnOff = 0;
int32 error = 0;
TaskHandle taskHandle = 0;
char errBuff[2048]={'\0'};
time_t startTime;
bool32 done=0;
// Channel parameters
char chan[] = "Dev1/ai0,Dev1/ai1,Dev1/ai2,Dev1/ai3,Dev1/ai4";
float64 min = -10.0;
float64 max = 10.0;
// Timing parameters
char clockSource[] = "OnboardClock";
uInt64 samplesPerChan = 1;
float64 sampleRate = 1000.0;
// Data read parameters
#define bufferSize (uInt32)1000
float64 data[100];
int32 pointsToRead = 1;
int32 pointsRead;
float64 timeout = 3.0;
int32 totalRead = 0;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
nTimer(UINT nIDEvent) 
