UR7HCTS2-U860-DR Semtech Corporation, UR7HCTS2-U860-DR Datasheet - Page 4

• Manufacturer Part Number: UR7HCTS2-U860-DR
• Description: High-Performance USB Touch Screen Controller / Digitizer
• Manufacturer: Semtech Corporation

Copyright Semtech 2000-2001
DOC7-TS2-U860-DS-101
The ScreenCoder
interface has the following features:
Touch detection
The IC periodically checks touch pressure applied to the panel. If there is no touch, the IC will not perform
measurements and will not send data to system. When touch pressure is detected, the IC further qualifies and
determines the amount of pressure. Semtech’s proprietary, patent-pending touch detection algorithm performs this
test very quickly, accommodating sensors with various plate-to-plate capacitances.
Touch Measurement
Position information is only collected if it has been determined that the touch pressure is sufficient for an accurate
reading. To obtain position information from the Resistive Touch Screen Sensor, the ScreenCoder
internal drivers (two pins for each driver) and four sense lines. During sampling, the drivers of the X-axis are
activated by setting one X-drive high and the other X-drive low. The drivers for Y-axis are set floating. This action
produces a voltage gradient across the touch screen's surface in the X direction. The internal A/D measures both
the voltage across the activated X-plane and the voltage potential between the planes. Next, the drivers for the Y-
axis are activated while the drivers for X-axis are set floating. Again, the internal A/D measures both voltage across
the activated plane and potential between the planes. The X and Y absolute position is obtained from these four
A/D measurements. The IC keeps measuring the touch pressure even while the positioning data is acquired. If
insufficient touch pressure is detected during sampling of the position, the current data set will be rejected.
Touch algorithm
Due to vibration and electrical noise, the raw data can not be used directly. Internal data processing delivers
consistent position accuracy and quick touch response.
Resolution
The ScreenCoder
resolution is 1000 points per direction. Resolution varies somewhat for different touch screen sensors, due to
voltage droop on connecting wires.
Touch screen from different makers
Operating parameters for the touch screens from different manufacturers vary depending on the size of the sensor,
material it is made from, and mechanical construction. The ScreenCoder
account, and adjusts automatically for plate-to-plate capacitance, intrinsic plate resistances, etc.
Buttons
The ScreenCoder
button press is reported when there is touch pressure on the panel. The left button is released when there is no
pressure on the panel. The right button is a physical button, and can be used individually.
TOUCH SCREEN SENSOR INTERFACE
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USB uses a built-in A/D converter to get the touch position. The maximum touch screen
USB implements both left and right buttons, however, there is no physical left button. Left
USB can acquire data from any 4- or 8-wire resistive touch screen sensors. The sensor
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USB takes these properties into
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USB uses four