I'm trying to attach an external hard drive to my 522. does it have to be formatted to work or can I use one which has data on it?
522 does not use EHD.
Only 211, 211k, 411, 612, 622, 722, 722k can use EHD.
When you attach a self powered EHD to any of these the receiver knows what to do.
Interesting, in the Record Plus menu on my 522 there is a button for "ERD Setup". Once I select it it gives options to either disable or enable "recordings to an external device".
Is this something different?
Yes...for the old Pocket Dish.