UR7HCTS2-U860-DR 查看數據表（PDF） - Semtech Corporation

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UR7HCTS2-U860-DR

High-Performance USB Touch Screen Controller / Digitizer

Semtech Corporation 

TOUCH SCREEN SENSOR INTERFACE

The ScreenCoderTM USB can acquire data from any 4- or 8-wire resistive touch screen sensors. The sensor

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 ScreenCoderTM USB uses four

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 ScreenCoderTM USB uses a built-in A/D converter to get the touch position. The maximum touch screen

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 ScreenCoderTM USB takes these properties into

account, and adjusts automatically for plate-to-plate capacitance, intrinsic plate resistances, etc.

Buttons

The ScreenCoderTM USB implements both left and right buttons, however, there is no physical left button. Left

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.

Copyright Semtech 2000-2001

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DOC7-TS2-U860-DS-101

www.semtech.com

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