A description of an xy game

As stated on the front cover of this manual, this is Atati's first X-Y game. What's the difference between an X-Y game and Atari's previous games? To answer this, let's first discuss our previous games.

1. The Raster-Type Game

All previous Atari video games utilized a raster-scan monitor. These games contained a monitor that internally produces signals that scan the beam across the face of the picture tube screen. The beam, as in your home TV, starts at the top left comer of the screen, moves horizontally across to the right of the screen, turns off, moves down a little while returning to the left of the screen, turns on, and again, moves to the right of the screen. This is repeated until the beam reaches the bottom right corner. The beam is then turned off while it is moved all the way back to the top of the screen, then the process is repeated over and over. The result is many horizontal lines (240 lines is typical in our raster games) on the surface of the screen, scanned so fast that the screen appears to be lighted all the time.

In these games, the game PCB electronic circuitry is synchronized with the beam and turns the beam on and off, as required to produce the appropriate game video.

2. The X-Y-Type Game

This type of game utilizes a monitor known as an X-Y monitor. In the X-Y game, the first thing you will notice is that the picture tube beam is not continuously scanned. Therefore, the game PCB does not contain a standard sync circuit. Instead of the beam being internally controlled by the monitor, the game PCB controls the location of the beam at all times. As in the raster-scan monitor, the yoke of the X-Y monitor deflects the beam. The picture of the X-Y game is produced by drawing vectors on the surface of the monitor screen. This is done by the vector generator circuitry of the game PCB. This circuitry locates the beam in steps. There are 1024 steps for the horizontal location of the beam, and 768 steps for the vertical location. Therefore, there are 786,432 resolution bits (768 x 1024) on the surface of the X-Y monitor screen. Since our typical raster-scan game has only 61,440 resolution bits (256 line bits x 240 lines), the X-Y game is capable of developing a picture with much finer detail.

The vector generator draws vectors on the monitor by turning the beam on while deflecting the beam horizontally and/or vertically. An increase of the horizontal deflection current moves the beam to the right. Decreasing this current moves the beam to the left. Increasing the vertical deflection current moves the beam up. Decreasing this current moves the beam down. Increasing both deflection currents simultaneously at the same rate results in a vector that slopes upward and to the right at a forty-five degree angle. By controlling the amount of horizontal and vertical deflection current, the vector generator is capable of "drawing" a line between any two given points on the monitor screen.

The X axis output of the vector generator is the horizontal axis of the monitor, while the Y axis is the vertical. The Z axis output of the vector generator controls the brightness of the beam. Without the brightness control, a short vector drawn in the same amount of time as a long vector would result in the short vector being brighter than the long vector.

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