Introduction

The MCP23S17 is a SPI Based Port Expander which can add 16 more digital I/O pins to your Arduino or Raspberry Pi. Thanks to the wide operating voltage of 1.8 – 5.5V,  you can add 5V I/O pins to the Raspberry Pi or 3.3V based Arduino thereby avoiding a level shifter and simplifying connections.

Hardware Required:

MCP23S17 Port Expander

Breadboard

Jumper Wires

Board Overview

The board consists of 2 Port Banks (A and B), a 3-way switch, power and SPI headers

3-Way switch is used to set the address of the Port Expander, the switch positioned towards ON sets the address as ‘0’. The image above sets the address as ‘7’

INT B Interrupt output for PortB

B.0 – B.7 Bidirectional I/O

INT A Interrupt output for PortA

A.0 – A.7 Bidirectional I/O

VCC Power supply pin for the MCP23S17, connect to a voltage source between 1.8V -5V

GND connect to ground of power supply

SO, SI, SCK & CS SPI Pins

RESET connect to ground to reset the port expander

Note: The silkscreen on Port A is reversed, meaning INT A actually is A.7 and A.7 actually is INT A

Enabling SPI on the Raspberry Pi

By default the SPI peripheral is not enabled, we cannot continue unless this is done first. Have a look at the tutorial by SparkFun on how to do this.

Interfacing the MCP23S17 Port Expander with the Raspberry Pi

Interfacing the MCP23S17 to the Raspberry Pi

Connections from Raspberry Pi to MCP23S17 Port Expander

Installing the Python Library

In order to get started the python library needs to be installed first. Run the following command in terminal to install the library

sudo pip install RPiMCP23S17

Sample Code

The below code will turn ON and OFF all the pins at an interval of 1 second.

from RPiMCP23S17.MCP23S17 import MCP23S17
import time

mcp = MCP23S17(bus=0x00, ce=0x00, deviceID=0x00)
mcp.open()

for x in range(0, 16):
    mcp.setDirection(x, mcp.DIR_OUTPUT)

print "Starting blinky on all pins (CTRL+C to quit)"
while (True):
    for x in range(0, 16):
        mcp.digitalWrite(x, MCP23S17.LEVEL_HIGH)
    time.sleep(1)
    for x in range(0, 16):
        mcp.digitalWrite(x, MCP23S17.LEVEL_LOW)
    time.sleep(1)

Further Reading

RPiMCP23S17 Github Repo