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Using a port expander as keypad controller

Posted: 27 Feb 2009     Print Version  Bookmark and Share

Keywords:STMPE801  port expander  keypad controller 

STMPE801 is an 8-bit general-purpose port expander device in the STMicroelectronics Port Expander Logic family. Its eight general purpose input output (GPIOs) are connected to the host system using a standard I2C connection.

This application note by STMicroelectronics explains how to control an 8*8 (64-key) matrix keypad using the eight internal GPIOs of a base-band processor and the eight GPIOs of the STMPE801 port expander. The simplified schematic for using STMPE801 as a keypad controller is provided by this document.

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 Base band 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

To minimise I2C traffic between the base band and the STMPE801, the GPIOs in base band (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.

View the PDF document for more information.

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