How do you mean?
Getting a pin takes two rounds if I read the rules right.
Round 1
Make an attack roll. If you hit, you start a grapple by putting a hold on the opponent and possibly dealing damage. You are now grappling.
Round 2
As an attack action you can do further damage to your opponent, pin him, break another's pin or escape a pin. Since it is an attack action as well, starting the grapple and starting a pin can't happen in one round unless you have a feat that allows it.
I'm pretty sure I did it right, I was reading up on it again to make sure while doing the round. Heck, I even said you had hold of his arm, making one cannon kind of useless.
Anyway, expect possibly spotty updates for a while, as I quit my job today.