heang,
So are you trying to figure out how you can begin the simulation of a waveform by clicking your mouse, or are trying to begin it when an input voltage reaches a threshold? Where is this input voltage coming from if you are not using hardware? If you want to produce a waveform once a mouse is clicked, you can use the
event structure to acheive this. If you are looking to produce the waveform once an input voltage reaches a certain threshold, I suggest checking out some of our DAQmx examples in the NI Example Finder (Help->Find Examples). Specifically look at the Acq & Graph Voltage-Ext Clk-Analog Ref.vi example to see how to trigger off analog thresholds. Hope this helps!
Brian T
Applications Engineer