Schematic

This is the 7800 Pokey cart. Along with the ROM chip there is an Atari Pokey sound chip which allowed some games to have a much better sound capabilities then the stock system provided. The Pokey chip is mapped to the address range $4000 to $7fff. The registers repeat every 16 bytes. One of the odd parts of this board is jumper W2. It allows pin 27(A14) of the ROM to be connected to either A14 or R/W. Connecting it to R/W would only make sense if it was a RAM chip, but then this would leave no place for a ROM on the board. The only thing I can think is that Atari intended to make a custom ROM chip for this board that contain either extra RAM or bankswitching hardware.