SX8674ICSTRT datasheet(13/64 Pages) SEMTECH

13 / 64 page

ADVANCED COMMUNICATIONS & SENSING

Rev 1 – 25

th July 2011

www.semtech.com

SX8674/SX8675/SX8676

Haptics Enabled Multitouch 4/5-Wire

Resistive Touchscreen Controller with Proximity Sensing

TOUCHSCREEN INTERFACE

4.1

Introduction

The purpose of the touchscreen interface is to measure and extract touch information like coordinates and

pressure. This is done in two steps, first an ADC measures the analog signal coming from the screen, and then

digital processing is performed to consolidate the data.

As illustrated below the chip’s touchscreen interface is compatible with both 4-wire and 5-wire touchscreens.

Touchscreen type is defined by parameter TSTYPE.

Figure 9 – Touchscreen Interface Overview

A 4-wire resistive touch screen consists in two (resistive) conductive sheets separated by an insulator when not

pressed. Each sheet is connected through 2 electrodes at the border of the sheet. When a pressure is applied

on the top sheet, a connection with the lower sheet is established.

Figure 10 – 4-wire Touchscreen

A 5-wire resistive touch screen consists in two (resistive) conductive sheets separated by an insulator when not

pressed. 4 electrodes are connected on the 4 corners of the bottom conductive sheet. They are referred as Top

Left (TL), Top Right (TR), Bottom Left (BL) and Bottom Right (BR).

The fifth wire (WIPER) is used for sensing the top sheet voltage. When a pressure is applied on the top sheet, a

connection with the lower sheet is established.

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