how I can calculte the time between two edges of square wave

[saqib]

I want to measure the time between to edges of the 6 square waves simultaneously. i.e. using the time function to calculate the T-on time of the waves and time period of the wave.

[LBoltzmann]

You didn't specify how you are obtaining you square waves, but if you are using Data Acquisition card from NI you can use the built in counters to determine the frequency/Period of your square waves. The following link has several examples of how to do this.

http://zone.ni.com/devzone/devzone.nsf/webcategories/33E541E2AEBC0B5986256786000FC83D?opendocument&node=DZ52329_US

If you already have the data you could use the Waveform Basic Trigger Detection VI to determine where the edges of your square wave occur and then compute the delta t from their places in the waveform array.