Prep the pineapple by peeling and slicing it into rounds about an inch thick.  I core the centers of the rounds with a small biscuit cutter about 2 inches in diameter but an apple corer would work here, too.  Set the cored rounds aside.  Preheat the oven to 350.  Make the cake mix according to directions and set aside.  In a 10 inch cast iron skillet over medium heat, melt together the brown sugar and the butter.  Remove it from the heat as soon as it's combined. 

Arrange the pineapple slices first in the bottom of the skillet.  Fill in all the remaining space with the black cherries.  If the cherries have any ice crystals on them, simply rinse them by the handful and give them a quick pat with some paper towels to get rid of the excess water. 

Pour the cake batter over the top and bake until a toothpick inserted into the center comes out clean, about 30 to 40 minutes.  Don't worry if it takes a little longer.  Using a platter larger than the circumference of the skillet, invert the cake once it has cooled for about 20 minutes.