Single cycle of Analog output

Hi all,

I want to generate a single cycle (as shown in the waveform graph) of analog output using PCI-6711 and then stop/pause the program.  I added a condition in the while loop that when i equal the waveform length, the program will break the while loop.  However, it doesn't work.  Reading by an oscilloscope, I always find that the analog output contains more pulses than what I define (or what shows on the waveform graph).  Does anyone have any suggestions that I should try?  

Thank you!