MK712SI Просмотр технического описания (PDF) - Integrated Circuit Systems
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MK712SI Datasheet PDF : 16 Pages
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I CR O C LOC K
MK712
Touch Screen Controller
Recommended Circuit
From
Microprocessor
14.318 MHz
+3.3V or +5V
22µF
0.1µF 0.1µF
RD
CS
WR
A0 - A2
D0 - D7
CLKIN
VDD
VDD
VDD
TOUCH
INT
XH
XL
YH
YL
To Power Management
To Interrupt Controller
X HIGH
X LOW
Y HIGH
To
Touch
Screen
Y LOW
GND
GND
GND
0.01µF 0.01µF 0.1µF 0.1µF
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.
MDS 712 I
6
Revision 100899 Printed 11/16/00
Integrated Circuit Systems, Inc.•525 Race St.•San Jose•CA•95126•(408)295-9800tel•www.icst.com
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