how to record a mic and an interface at the same time with 2 channels

i am about to try a new recording technique in Logic. i want to have my acoustic guitar plugged into my interface and record through that but at the same time have my acoustic mic'ed at the fret board and record that on a different channel then blend the two wave forms together. how do i get both channels to record at the same time on different channels?

if thats confusing, let me explain further. i have my guitar plugged into the first input channel on my interface and the plugged in guitar is set to track 1 in logic, i have my mic plugged into the second input channel on my interface and it is set to track 2 in logic. but when i try and record, it only records track one, the plugged in guitar and not the mic. how do i get both to record at the same time?