I've been there twice within the last year. With one exception, the Carnival ships I've seen there used Puerta Maya Pier. If that gets filled, they may dock you at the Transportacion Maritima Mexicana (TMM) Pier, a few hundred yards north.
The pier complex is located about 5KM (3.5 miles) south of the main town. There is also a cruise ship pier in the town, used by other lines.
I may dwell on the land, but I live at sea!
Sensation 2/03 I disembarked, but never really left the ship.
Sensation 04/05 The vessel made me do it!
Summit 03/06 to Hawaii, Where God left his fingerprints, in memory of Margaret.
Carnival Freedom (March 08)
\X\Mercury (January 09)