Arbitrary Waveform Generator

OK, thanks for the input. Anyway, I wrote up a script that takes a Matlab waveform and converts it to the intel hex file. I get great sinewaves, modulated sinewaves, triangle waves, etc. Unfortunately, my pulses look like the attached pictures. Before I start hacking away at my DAC code, does anyone have a clue what might be happening? These were supposed to be continuous pulse trains, 4us long, but instead i get short pulses.