AN2421 datasheet(3/6 Pages) STMICROELECTRONICS

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AN2421

Design objectives

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Design objectives

The keyboard controller presented in this application note complies with the following design

objectives:

●

Implementation of an 8*8 keypad controller using 8 GPIOs from the Baseband and 8

GPIOs from the STMPE801

●

Requires no external interrupts

●

Minimum traffic on the I2C bus

●

Ability to support hot-key (wake-up from suspend) features

Keypad scanning operation

The rows (X-n) are used as inputs and are pulled up to VCC using a weak pull-up resistor

(47kOhm). The columns (Y-n) are used as outputs and are normally driven to VCC. An X-Y

matrix keypad works in the following sequence:

Y-0 is driven to GND.

KPC Software scans X-0 to X-n. A "LOW" indicates that key Y-0, X-n is pressed.

Y-0 is driven to VCC. Scanning of column 1 completes.

Proceed to scanning of column Y+1.

To minimize I2C traffic between the baseband and the STMPE801, the GPIOs in baseband

(BB_GPIO) are used as inputs and the STMPE801 GPIOs (801_GPIO) are used as

outputs. This enables KPC Software to operate without causing the STMPE801 to return

interrupts. There is no reading operation from the STMPE801.

AN2421 Datasheet(PDF) 3 Page - STMicroelectronics