13

MK715

Recommended Circuit

When the screen is untouched, the Y plate is driven high and the X plate is driven low. When the screen is touched, the

X plate is pulled high, which is detected by the MK715. This initiates a conversion, as long as conversions at rate

(ENCONR) are enabled. Some de-bounce is provided by the time constant of the screen decoupling capacitors

combined with the screen resistance. However, once conversions have started, pen bounce will not be detected until

after the current X or Y points have been taken.

If the pen is lifted during a conversion, this will also not be detected until the conversion is complete.

Pen Bounce

TOUCH#

INT

PL

XL

XH

YH

GP

SK

CS

D0

DI

GND

VDD

X2

X1

To Interrupt Controller

To Microcontroller

To Power Management

CAP3

CAP2

CAP1

YL

CLKOUT

To Touch

Screen

From

Microprocessor

32.768 kHz

Crystal

+ 3.3V or +5V

Analog Voltage

All 0.01mF

0.01mF

1mF

0.01mF

The capacitors connected to CAP1 and CAP3 must be low leakage, ceramic type capacitors.

100kW 0.01mF

470 pF