LPC47M112_07 SMSC [SMSC Corporation], LPC47M112_07 Datasheet - Page 130

• Manufacturer Part Number: LPC47M112_07
• Description: Enhanced Super I/O Controller with LPC Interface
• Manufacturer: SMSC [SMSC Corporation]

Enhanced Super I/O Controller with LPC Interface
Datasheet
27 GAME PORT LOGIC
The LPC47M112 implements logic to support a dual game port. This logic includes the following for each game port:
two 555 timers, two game port RC constant inputs (x-axis and y-axis), two game port button inputs and game port
interface logic. The implementation of the Game Port uses a simple A/D converter constructed from a 555 timer to
digitize the analog value of a potentiometer for the x-axis and y-axis of the joystick.
The figure below illustrates the implementation of the game port logic in the LPC47M112.
Game software will write a byte to the game port to reset it, and then poll (read) the port until the x and y-axis RC time
constant pins (TIMA,B) time out (return to zero). The elapsed time indicates the resistance value of the potentiometer
and in turn, the position of the joystick.
The figure below illustrates the timing of the game port signals. The 556 timers will reset the outputs (OUTA,B) to
zero and the RC constant (TIMA,B) pins to zero when the RC constant (TIMA,B) inputs reach 2/3 of VREF as shown.
VREF is the voltage on pin 44, which is either 5V or 3.3V. See the “VREF Pin “ section.
SMSC DS – LPC47M112
JOYW
JOYR
Game Port
Register
Internal To LPC47M10x
D0
D1
D2
D3
D4
D5
D6
D7
JOYW
TIMA,B
OUTA,B
JOYR
OUT1A
OUT1B
TRIG1A
TRIG1B
OUT2A
OUT2B
TRIG2A
TRIG2B
DATASHEET
t1
556
556
TIM1A
TIM1B
TIM2A
TIM2B
Page 130
J1X
J1Y
J2X
J2Y
J1B1
J1B2
J2B1
J2B2
Vcc = 5V
X-Axis
Y-Axis
X-Axis
Y-Axis
VREF
2
3
Internal To Joysticks
VREF
Vcc = 5V
Vcc = 5V
Vcc = 5V
Vcc = 5V
Joystick 1 Button 1
Joystick 1 Button 2
Joystick 2 Button 1
Joystick 2 Button 2
Joystick 1
Joystick 2
Rev. 02-16-07