PC87373 datasheet(125/174 Pages) NSC

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10.0 Game Port (GMP)

10.1 OVERVIEW

This chapter describes a generic Game Port. For the implementation used in this device, see Section 3.16.1 on page 70.

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

of these game devices at any specific moment.

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

game device inputs these commands passively, by indicating several status parameters that can be captured by the system

via the Game Port. A joystick is a commonly used game device.

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 34 shows the basic system configuration of the Game Port.

Figure 34. Game Port System Conﬁguration

10.2 FUNCTIONAL DESCRIPTION

10.2.1 Game Device Axis Position Indication

A typical game device has the following interface pins:

X-axis position indicator

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 shown in Figure 35.

Such a mechanism is implemented for each axis line of each game device.

Figure 35. 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

External Components

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