Preheat oven to 350 degrees. Melt butter in 13 x 9 x 2 inch pan. Sprinkle brown sugar evenly in pan. Arrange pineapple slices on sugar. Put cherry halves in the center of each pineapple slice. Prepare cake as directed on package. Instead of water use pineapple juice. Turn batter over fruit and spread evenly. Bake at 350 degrees for 43-48 minutes or until cake is done. Insert toothpick in center to see if it is done. Let stand 5 minutes. Toss topping. Loosen cake from pan and turn upside down on platter.