Selftest Switch

Figure 4-2 Game Block Diagram

The game's composite video signal produces only four video levels instead of the continuous shades of grey seen on a home TV screen. The video levels are light grey, grey, white, and black.

On the game PCB schematic diagram, the symbol "P" (appearing at various inputs of integrated circuit devices) indicates a connection of +5 volts DC through a pullup resistor (see Figure 4-3). For easy reference, the game PCB is divided into grid sections. Along the short side of the board, these sections are identified by letters A through E. Along the long side of the board, the numbers 1 through 9 are used. For example, sheet 2 of Figure 4-3 illustrates the mic-roporcessor E3 at the right side of the drawing. The microporcessor is found at coordinates E and 3 on the PCB.

A monitor interface adapter, which is controlled by the microprocessing unit (MPU), performs the following functions:

• Produces all horizontal and vertical sync functions.

• Generates video for all objects.

• Generates all sound.

The MPU reads player pots through this adapter by measuring the charge rate of a capacitor charging through each pot.

Input interface adapters read switches (option, player control, and start switches); and function as outputs for the LED control, and the coin lockout con trol.

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