There are several Open Source HDL projects that describe the hardware required to implement classic arcade games on an FPGA. These designs allow for learning, exploration, and a deep understanding of how simple 8 bit systems work. Learning the ins and outs of these classic arcade games is not only fun, but it provides a very solid foundation for building your own systems, whether it be games or gadgets.
This is a quick list of sites that have designs that can be downloaded and studied. Pac-Man is the first game to be ported to the Papilio Arcade Kit but any game that uses less than 40KB or memory can be ported.
The PacMan project can be downloaded from the Papilio Arcade project page.
The available source code is the hardware image for both the Frogger and Scramble. They only have a minor difference in hardware configuration. There is a constant at the scramble_top.vhd that controls which configuration to select.
constant I_HWSEL_FROGGER : boolean := TRUE;
The current source code is configured for Frogger hardware. Just set the I_HWSEL_FROGGER to FALSE to select the Scramble configuration.