Adafruit-MCP23008-library

# Adafruit MCP23008 Library (ARCHIVED)

**This library is archived and no longer maintained. Please use the replacement library:**

[Adafruit MCP23017 Arduino Library](https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library)

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This library provides basic functionality for interfacing with the Microchip MCP23008 8-bit I/O expander using the Arduino platform.

## Installation

1.  **Download:** Click "Download Source" in the top right corner of this page.
2.  **Install:** Follow the instructions in the Adafruit Arduino Libraries tutorial: [http://www.ladyada.net/library/arduino/libraries.html](http://www.ladyada.net/library/arduino/libraries.html).  Create a folder named `Adafruit_MCP23008` in your Arduino libraries directory and place the contents of the downloaded archive there.
3.  **Dependencies:**  This library requires the [Adafruit BusIO library](https://github.com/adafruit/Adafruit_BusIO).  Please install it as well.

## Functionality

This library provides the following basic functionality:

*   Setting pin directions (INPUT or OUTPUT).
*   Reading digital input values.
*   Writing digital output values (HIGH or LOW).
*   Enabling/disabling internal pull-up resistors.

**Limitations:**

*   This library is considered beta and may not be fully optimized.
*   The interrupt capability of the MCP23008 is **not** currently supported.

## Wiring

Connect the MCP23008 to your Arduino as follows:

*   **Pin 1 (SCL):** Arduino Analog 5 (I2C clock)
*   **Pin 2 (SDA):** Arduino Analog 4 (I2C data)
*   **Pins 3, 4, 5 (A0, A1, A2):** Ground (Address selection - all grounded sets the I2C address to 0x20)
*   **Pins 6 (RESET) & 18 (VDD):** 5V (Power and reset disable - tying RESET high disables the reset function)
*   **Pin 9 (VSS):** Ground (Common ground)
*   **Pins 10-17 (GP0-GP7):** Digital Input/Output pins

**Note:**  The I2C address of the MCP23008 can be configured using pins A0, A1, and A2.  Consult the datasheet for address selection details.

## Datasheet

For more detailed information about the MCP23008, please refer to the datasheet:

[http://ww1.microchip.com/downloads/en/DeviceDoc/21919b.pdf](http://ww1.microchip.com/downloads/en/DeviceDoc/21919b.pdf)

## Contributing

Pull requests are welcome!  Please feel free to contribute improvements and bug fixes.  However, note that this library is archived, so contributions may not be actively reviewed.