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9.0

Game Port (GMP)

9.1

OVERVIEW

This chapter describes a generic Game Port. For the implementation used in this device, see the

Device Architecture and

Conﬁguration chapter.

The Game Port monitors the interface of up to two game devices, and provides data that can be used to determine the exact

momentary status of these game devices.

A game device is an instrument used for giving commands to a PC, usually to control a game executed on that PC. A Joystick

is a commonly used game device. These commands are given by the game device in a passive manner, by indicating sev-

eral status parameters that can be captured by the system via the Game Port.

The status of a game device includes the following parameters:

Button status (pressed/released) of up to two buttons per game device

Horizontal (X-axis) position indicated by the game device

Vertical (Y-axis) position indicated by the game device.

Figure 27 shows the basic system configuration of the Game Port.

Figure 27. Game Port System Conﬁguration

9.2

FUNCTIONAL DESCRIPTION

9.2.1

Game Device Axis Position Indication

A typical game device has the following interface pins:

an X-axis position indicator

a Y-axis position indicator

one or two button status indicator(s).

The X and Y axis indicators are fed into the Game Port via pins JOYnX and JOYnY, respectively, where ‘n’ indicates the

game device number. The status indicators of buttons 0 and 1 are fed into the Game Port via JOYnBTN0,1, respectively.

The X and Y axis position indication mechanism of each game device includes external components, as seen in Figure 28.

Such a mechanism is implemented per game device axis line.

Figure 28. Game Device Axis Position Indication Mechanism

Game

Port

Game

Device

Game Device

Interface

X-Axis

Y-Axis

Button 1

Button 0

Game

Device

Game

Device A

Circuitry

X-Axis

Y-Axis

Button 1

Button 0

RCX

RVX

Game

Port

JOYnX

JOYnY

Game Device

X/Y-Axis Varying

Waveform Shaping Circuit

Pins

Resistor

X/Y-Axis

Circuit

Discharge

Control

X/Y-Axis

Indicators

Input

Path

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