Right, left, forward and reverse tank motions are handled through a joystick control brought into an I/O port. Push buttons at the top of each joystick provide the tank fire controls and are also brought into an I/O port. The audio and attention-getting LED flashers are produced by firmware through an I/O port on the CPU. All in all, 20 of the 32 available I/O bits are used for this tank game.
The prototype version of the tank game uses PROM to store the program. This permits changes to be easily made while field testing before committing to the masked ROM MK3851 PSU used in the production version (Fig. 13). When the system is ready for volume production, the PROM can be removed and the MK3861 PIO can be replaced in the same socket with the MK3851 PSU to reduce production cost.
An extension of the design approach used in Tank Squadron could be applied to other games by separating the electronics into game dependent and game independent circuitry. Fig. 14, for example, shows a possible generalized cartridge based game design using this approach. The game dependent cartridge contains the background pattern, constant patterns, and game program for each game. The PSU in the game independent section may contain commonly used subroutines called by the PSU in the cartridge.
Pinball Games
These games generally represent less complexity than the video game hence may be handled in many cases by a single chip–namely the new MK3870 microcomputer. Fig. 15 shows a pinball machine completely controlled by an MK3870. Common inexpensive decoders and multiplexers may easily expand the 32 I/O bits present on the MK3870 to as many as needed to operate 7-segment displays, drive bumpers and lights and detect ball paths.
Another example of a game of less complexity than the video game is shown in Fig. 16–the F8 based chess playing computer. MK3870, results in a machine which will play a credible game of chess. The external 256 x 8 RAM is addressed through an I/O port on the MK3870 and provides additional RAM beyond the 64 bytes already in the MK3870.
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