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MK712SILFTR

TOUCH SCREEN CONTROLLER

Integrated Device Technology 

MK712

TOUCH SCREEN CONTROLLER

Recommended Circuit

TOUCH SCREEN CONTROL

Pen Bounce

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 MK712. This initiates a conversion (as long as periodic

conversions 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 both the X and Y points have been taken.

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

indicated by a point with the correct Y coordinates, but minimum (for that screen) X coordinates.

Screen Decoupling

The component values suggested should give excellent results. However, for screens with a high resistance

operating at a high conversion rate, extra interrupts may be issued. This is because the time constant of the screen

decoupling capacitors and screen resistance is high, resulting in the screen appearing to be untouched and then

touched between conversions. These extra interrupts can be eliminated by reducing the size of the screen

decoupling capacitors on pins XH, XL, YH, and YL. This will, however, slightly reduce the noise rejection, which

could decrease the accuracy of the conversion.

IDT™ TOUCH SCREEN CONTROLLER

6

MK712

REV N 051310

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