How to sample a sawtooth waveform

I am using Altera DSP Board and try to sample a sawtooth waveform from the oscilloscope. So, the analog signal is coming from the output of the oscilloscope and go into the A/D converter on the board. Then I have to sample the lowest point, the highest point and the middle point and store these data in the memory. Do you have any idea to do that?

Thanks a lot!