The MCP23017 is a 16-bit, general purpose parallel I/O port expander for I2C bus applications. 

The 16-bit I/O port functionally consists of two 8-bit ports (PORTA and PORTB). The MCP23017 can be configured to operate in 8-bit or 16-bit modes

Features

• 16-bit remote bidirectional I/O port 
  - I/O pins default to input
• • High-speed I2C™ interface (MCP23017)
  - 100 kHz
  - 400 kHz
  - 1.7MHz
• Three hardware address pins to allow up to eight devices on the bus
• Operating Voltage: 1.8V to 5.5V

Download:

• Datasheet
• Tutorial of using MCP23017 with Arduino
• How To Use A MCP23017 I2C Port Expander With The Raspberry Pi