I have mathprint on and my displayed answers are all stacked fractions, however I can't input them that way without doing the ALPHA F1 key strokes. I know at one time I could input them automatically which made it so much easier to double check that I had everything inputed correctly as it was in the problem epcially on longer equations (having to count up () to make sure you have the right number in a huge equations is very tiring...)

hopefully someone knows what I'm talking about I'm pretty sure the TI 84 plus C does stacked fractions and such automatically as you input them even when using the / key.