How to generate a pulse of 5 V -ve polarity in synchronis​ation with a 10 v input using PCI 6251 DAQ board

Question

HI
I want to generate a 5V -ve polarity pulse to trigger my IEEE 1394 camera using an PCI 6251 (scb68 pin E) device, furthermore I am reading a standard Vsync signal from a SVGA port which is 10 v.
Now I want to synchronise the image capture of an IEEE 1394 camera with the Vsync signal so that camera is triggered to capture at every 4th Vsync signal (which is 50HZ.). Presently I am able to read the Vsync signal and also generate the -5 v signal But the Daq board generates a continues -5v signal while I want a 1 ms pulse (for every 4th Vsync).
Also this 5 v signal is generated even if the vi is stopped running.
Can anybody guide me so this problem can be solved.
Thanks a lot in advance
Shri

Answer 1

You can use the Write function, that is you can use the 10 volt signal as a trigger for the task, and when you get this trigger, the task starts and generate (writes) a waveform you defined in an array ("data", in the example).
Something like this..
DAQmxCreateTask("",&taskHandle);
DAQmxCreateAOVoltageChan (taskHandle, clokSource, your_sampling_freq, -10.0, 10.0,
DAQmx_Val_Volts, "");
DAQmxCfgSampClkTiming (taskHandle, clockSource, SAMPLING_RATE,
DAQmx_Val_Rising, DAQmx_Val_FiniteSamps,
samp_to_read);
DAQmxCfgAnlgEdgeStartTrig (taskHandle, input_channel, DAQmx_Val_RisingSlope, 9.0);
DAQmxWriteAnalogF64 (taskHandle, 1000, 0, 10.0,
DAQmx_Val_GroupByChannel, data, //data contain a pulse
&samp_per_channel, 0);
DAQmxStartTask(taskHandle);
// and then you create a loop....
For example you can specify data to be like this:
data[0] = -5;
for(i=1;i<1000; i++){
data[i] = 0;
Tell me if you need more help.....
bye