© 2006 Microchip Technology Inc.

DS01043A-page 1

AN1043

INTRODUCTION

GPIO expanders provide easy I/O expansion using

standard serial interfaces. GPIO products are used to

increase the I/O on an MCU or provide remote I/O

using a serial interface.

This application note discusses the feature set and use

of the MCP23X08/17 (8-bit and 16-bit) GPIO Expand-

ers.

The MCP23X08 are 8-bit GPIO Expanders:

• MCP23S08: SPI Interface

The MCP23X17 are 16-bit GPIO Expanders:

• MCP23S17: SPI Interface

The functions and features of the MCP23X08 and

MCP23X17 are basically the same, except where

otherwise noted.

FEATURES

This application note discusses some of the features of

the MCP23X08/17 and how they may be used in an

application:

• I/O Port Description

• 8/16-Bit Mode (MCP23X17 only)

• Interrupt Features

- Mapping Interrupts

- Mirroring Interrupts (MCP23X17 only)

- Servicing Interrupts

• Internal Address Pointer Control

• Hardware Address Pin on SPI

I/O PORT DESCRIPTION

The I/O port is highly configurable for maximum

flexibility. Figure 1 is a simplified block diagram of an

I/O port pin. The port can either drive logic levels on the

pin, or read logic levels from the pad. The level on the

pad can be read at any time, regardless if the pin is

configured as an input or an output.

The IODIR register controls the direction of the pins

(input or output). More specifically, the IODIR registers

simply enables/disables the output driver. When the

driver is activated (IODIR = 0), the pad is driven to the

state in the latch register (OLAT). When deactivated

(IODIR = 1), the driver is high impedance.

The I/O port has multiple, individual configurations.

Each pin can

…

•

disabled (high impedance)

•

is enabled and the value in the latch is driven on

the pin.

•

•

accomplished by clearing the output latch (OLAT)

bit to a zero and using the direction register

(IODIR) to set the level on the pin. A pull-up

resistor is required to pull the pin to voltage when

the pin is an input

- To drive a 0: configure the pin as an output

(IODIR = 0) so the port drives whatever is in

OLAT (logic 0 in this case)

- To float a 1: set the pin as an input

(IODIR = 1). The output driver is disabled

and the pull-up resistor pulls the pin to a

logic 1

Author:

Pat Richards

Microchip Technology Inc.

Unique Features of the MCP23X08/17 GPIO Expanders