STMPE812ABJR Datasheet STMPE812ABJR | P1-P3

December 2010 Doc ID 18161 Rev 1 1/35

AN3301

Application note

S-Touch

STMPE812A: a hardware and software guide

Introduction

The STMPE812A is a 4-wire resistive touchscreen controller with an integrated 4-bit port

expander. The touchscreen controller is designed to be fully autonomous, requiring only

minimal CPU intervention for sampling, filtering and preprocessing operations.

The purpose of this document is to highlight the guidelines and information complementary

to the datasheet that is necessary for a proper operation of the STMPE812A device in

applications.

The first part of the document highlights information on the hardware. This includes external

components/connectivity, power, PCB design and etc.

The second part of the document focuses on information in software in which programming

reference codes are shown. This part is to be used in conjunction with the STMPE812A

software library available in www.st.com.

www.st.com

Contents AN3301

2/35 Doc ID 18161 Rev 1

Contents

1 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 Typical application circuit and external components . . . . . . . . . . . . . . . . . 5

1.2 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.1 Power sequence (fail safe) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3 Power modes transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.4 Touchscreen tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4.1 Track resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.5 Noise prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.6 Noise filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.7 PWM controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.8 ADC controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.9 GPIO output configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.9.1 Push-pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.9.2 Open drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1 Touchscreen controller acquisition modes . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1.1 Data acquisition by internal timer (ACQ_mode “00”) . . . . . . . . . . . . . . . 13

2.1.2 Data acquisition by ACQ command (ACQ_mode “01”) . . . . . . . . . . . . . 14

2.1.3 Data acquisition by host read control (ACQ_mode “10”) . . . . . . . . . . . . 14

2.2 Embedded data valid bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3 Pen down interrupt mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.4 TSC_DATA read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.5 Touchscreen controller sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.6 Programming guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.6.1 Touchscreen initialization and interrupt handling (pen down mode) . . . 19

2.6.2 Touchscreen initialization and interrupt handling (normal interrupt mode)

2.6.3 GPIO initialization and interrupt handling . . . . . . . . . . . . . . . . . . . . . . . 28

2.6.4 ADC initialization and interrupt handling . . . . . . . . . . . . . . . . . . . . . . . . 29

2.6.5 PWM initialization and interrupt handling . . . . . . . . . . . . . . . . . . . . . . . 32

3 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

AN3301 List of figures

Doc ID 18161 Rev 1 3/35

List of figures

Figure 1. Typical application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 2. Track resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 3. Noise prevention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. PWM LED driving configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5. GPIO push-pull configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 6. GPIO open drain configuration (output low) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 7. GPIO open drain configuration (output high) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 8. Data acquisition by internal timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 9. Data acquisition by ACQ command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 10. Data acquisition by host read command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 11. TSC data register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 12. Touchscreen controller sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P33 P34-P35

STMPE812ABJR

Mfr. #:

Buy STMPE812ABJR

Manufacturer:

STMicroelectronics

Description:

Touch Screen Controllers Touchscreen cntrlr S-Touch

Lifecycle:

New from this manufacturer.

Delivery:

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STMPE812ABJR