Different types of PONG systems
When it is time to sort
the existing PONG systems, it is interesting to differenciate several
types of systems, depending on the technology used.
There are four types of PONG systems.
1) Analog systems
Unlike the title says, analog games always use digital signals, but generated by analog circuits. In other words, these games can be represented by a block diagram where the blocks would communicate using digital signals although each block would be designed with analog components. Such analog systems store the game parameters (ball and paddle positions and dimensions, game speed, etc) as variable voltages in capacitors. They are most of the time quite unstable and deliver a quite low quality video signal. The typical example is the Magnavox Odyssey, which displays a very unstable central line. All of its functions communicate through digital signals, but are made with analog components. It is quite easy to recognise an analog system by the effects of external perturbations. As a matter of fact, they can be perturbated by touching the pins of those capacitors storing game parameters, which results in drifts on the screen: ball deviation, strange shape of the ball, paddles or central line, unstable picture, etc.
2) Digital systems
Digital systems use digital components containing one or a few elementary functions: logic gates (AND, OR, NOT, etc.), counters, comparators, etc. These functions are available in two formats: TTL (chips of the 74xx series and derivates) and CMOS (chips of the 4000 series). Pure digital games use a large number of them, but home systems, which are mostly digital, also used analog components to replace several digital functions and reduce the production costs. Full digital games cannot be perturbated like analog games because the digital signals are represented by voltages which can vary more or less without altering the logical level they represent. As explained above, analog games store the game parameters as variable voltages in capacitors. Changing the voltage in a capacitor by touching its pins can alter the game parameter stored in it and result in strange effects on the screen. This cannot happen in full digital games because these parameters are encoded in binary format, a number of 1's and 0's respectively represented by a 5-volt and a 0-volt potential. Altering these signals a little bit will make no effect because any voltage around 5 volts will always be considered as a logical 1 and any voltage around 0 volt will also be considered as a logical 0. Full digital games were extremely reliable and of much better quality than most home games which used mixed signals.
3) Systems with a dedicated chip
Those systems used very few components because most of the circuitry of a Ball and Paddle game has been integrated into a single chip. This technology was much cheaper than the previous ones, and so, commonly used. Those chips are commonly referred as 'PONG in a chip' devices and are listed in the PONG in a Chip page. The most successful ones were made by General Instruments and National Semiconductor. Atari also used its own chips, but never made them available to other manufacturers
4) Programmed systems
Although we never found such a system made in the 1970s, there is a last type of PONG system: programmed systems. Instead of using a dedicated chip, those systems use software programmed games. The software is very small, and is either stored in an external memory and run by a microprocessor, or simply stored in a microcontroller (a component which combines microprocessor, memory and interfacing circuitry). Original systems based on this technology are not known for sure, but two of them are believed to be using it: the Coleco Telstar Arcade (which uses the same MPS-7600 chip in its cartridges), and the Atari Video Pinball. The only real example that we can give is a small key ring which encloses a LCD system offering a simple PONG game. Of course, we could include PONG games for computers, but in that case, we are not talking about PONG systems.