LPC47M14X datasheet(124/205 Pages) SMSC

124 / 205 page

SMSC DS – LPC47M14X

Page 124

Rev. 03/19/2001

Game Port Register

<GAME_PORT>+0h

System I/O Space

Default Value:

00h

VTR POR

Attribute:

Read-Only

Size:

8-bits

Button #2

Joystick 2

(J2B2)

Button #1

Joystick 2

(J2B1)

Button #2

Joystick 1

(J1B2)

Button #1

Joystick 1

(J1B1)

Y-Axis

Joystick 2

(OUT2B)

X-Axis

Joystick 2

(OUT2A)

Y-Axis

Joystick 1

(OUT1B)

X-Axis

Joystick 1

(OUT1A)

The game port register is a read-only register. However, writing to the game port resets the RC time constant pins

(TIMA,B) to zero. The reset of the time constant pins occur on the “back” edge of the write signal (when the write

signal goes from its active state to its inactive state).

The game port read (JOYR) will be an IO read to the address programmed into the base IO address in Logical

Device 9.

The game port write (JOYW) will be an IO write to the address programmed into the base IO address in Logical

Device 9.

Minimum Rise Time

The fastest rise time on the RC constant pins (minimum RC time constant) for the game port is 20usec.

6.19.1

Power Control Register

Bit 2 in the Power Control Register (CR22) is the power control bit for the game port. This bit has the same function

as the activate bit for logical device 9 and shadows the activate bit. The activate bit also shadows the power control

bit 2.

6.19.2

VREF Pin

The LPC47M14x has a reference voltage pin input on pin 44 of the part. This reference voltage can be connected to

either a 5V supply or a 3.3V supply. It is used for the game port.

The reference voltage is used in the game port logic so that the joystick trigger voltage is 2/3 VREF where VREF is

either 5V or 3.3V. This is to preserve joystick compatibility by maintaining the RC time constant reset trigger voltage

of 3.3V (nominal) with VREF=5V (nominal), if required.

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