Arduino library for Microchip MCP23017 IO expander using I2C.
The IO expander gives you additional 16 Inputs or Outputs.
The chip have to banks, GPAx (pin 0 ... 7) and GPBx (pin 8 ... 15).

          --------    
GPB0 (0) -|1   28|- GPA7 (15)
GPB1 (1) -|2   27|- GPA6 (14)
GPB2 (2) -|3   26|- GPA5 (13)
GPB3 (3) -|4   25|- GPA4 (12)
GPB4 (4) -|5   24|- GPA3 (11)
GPB5 (5) -|6   23|- GPA2 (10)
GPB6 (6) -|7   22|- GPA1 (9)
GPB7 (7) -|8   21|- GPA0 (8)
VDD  (+) -|9   20|- INTA
VSS  GND -|10  19|- INTB
NC       -|11  18|- RESET (+)
SDK      -|12  17|- A2
SDA      -|13  16|- A1
NC       -|14  15|- A0
          --------

Advices

• set the RESET pin (18) to VDD (+)
• set the Address pins (15 ... 17) for address 0 set all to GND

Here is a simple example which shows the capabilities of the library.
Attach two LED's to pin 0 and 1 (bank GPA0 and GPA1) and two buttons to pin 8 and 9 (bank GPB0 and GPB1).

#include "MCP23017.h"

MCP23017 ioExpander;

void setup() {
	ioExpander.begin();
	ioExpander.pinMode(8, INPUT_PULLUP);
	ioExpander.pinMode(9, INPUT_PULLUP);
	ioExpander.pinMode(0, OUTPUT);
	ioExpander.pinMode(1, OUTPUT);
	ioExpander.digitalWrite(0, LOW);
	ioExpander.digitalWrite(1, LOW);
	}

void loop() {
	ioExpander.digitalWrite(0, !ioExpander.digitalRead(8));
	ioExpander.digitalWrite(1, !ioExpander.digitalRead(9));
	}

Create an IO expander object.

MCP23017(uint8_t i2cAddr = 0);

• i2cAddr 0 ... 7, default 0, see data sheet

Example

MCP23017 ioExpander;

void begin(TwoWire &wire = Wire);

• spi set optional I2C class to use (I2C, I2C1, ...)

Initialize the I2C communication of the IO expander.
This must done in setup()

Example

setup() {
  ioExpander.begin(); // default I2C class
  ioExpander.begin(I2C1); // use I2C 1 class
  }

Set the pin mode.

void pinMode(uint8_t pin, uint8_t mode);

• pin digital input (0 ... 15) to read
• mode mode INPUT / INPUT_PULLUP / OUTPUT

Example

ioExpander.pinMode(8, INPUT_PULLUP);
ioExpander.pinMode(0, OUTPUT);

Read a digital pin. Returns the value (HIGH / LOW, 0 / 1, true /false).

uint8_t digitalRead(uint8_t pin);

• pin digital input (0 ... 15) to read

Example

uint8_t input1 = ioExpander.digitalRead(8);

Write to a single digital output.

void digitalWrite(uint8_t pin, uint8_t value);

• pin digital output (0 ... 15) to write

Example

ioExpander.digitalWrite(0, LOW);

Setup the interrupts.

void interruptSetup(uint8_t mirroring, uint8_t open, uint8_t polarity);

• mirroring OR both INTA and INTB pins
• openDrain set the INT pin to value or open drain
• polarity set LOW or HIGH on interrupt

Set the interrupt pin and it's mode.

void interruptPin(uint8_t pin, uint8_t mode);

• pin interrupt pin (0 ... 15)
• mode mode CHANGE, FALLING, RISING

Return the last pin an interrupt occurs. Returns the number of the pin.

uint8_t lastInterruptPin();

Returns the value of the last interrupted pin(HIGH / LOW, 0 / 1, true /false).

uint8_t lastInterruptPinValue();