how to sample with midi clock

Hi Everyone,

I am a newbie, just got an sp-808EX used, and am trying to figure out if i can sample a loop that is being played to midi clock. I have the SP-808 running master clock and another sequencer (slave) triggering a keyboard sequence. I want to sample exactly 4 measures of the keyboard sequence without having to edit the sample after. Is there a way to sample midi measures exactly?

Can anyone help me to do this?

Thanks,
Mike