How to Use MCP23017: Examples, Pinouts, and Specs

The MCP23017 is a versatile I/O expander from Microchip that allows a microcontroller to control up to 16 additional digital inputs or outputs via a two-wire I2C serial interface. This component is particularly useful in applications where additional I/O pins are needed, such as in button matrices, LED control, or when interfacing with multiple sensors. Common applications include home automation systems, industrial controls, and hobbyist projects where expansion of I/O capabilities is required.

• Supply Voltage (VDD): 1.8V to 5.5V
• Input/Output Sink Current (IOL): 25 mA (max)
• Input/Output Source Current (IOH): -25 mA (max)
• Operating Temperature: -40°C to +125°C
• Communication Interface: I2C serial interface
• I2C Addresses: 8 different addresses selectable via hardware (0x20-0x27)

1. Power Connections: Connect VDD to the microcontroller's power supply (1.8V to 5.5V) and VSS to ground.
2. I2C Connections: Connect SCL and SDA to the corresponding I2C clock and data lines on the microcontroller. Pull-up resistors may be required on these lines.
3. Address Selection: Set the hardware address by connecting A0 and A1 to either VDD or VSS. This will determine the I2C address of the MCP23017.
4. Reset (Optional): Connect the RESET pin to a digital output on the microcontroller if hardware reset functionality is desired.
5. I/O Configuration: Configure the I/O pins (GPA0-GPA7 and GPB0-GPB7) as inputs or outputs by writing to the IODIRA and IODIRB registers.

• Ensure that the power supply voltage is within the specified range for the MCP23017.
• Use pull-up resistors on the I2C lines as required by the microcontroller's I2C specification.
• Avoid exceeding the maximum current ratings for the I/O pins.
• When using the MCP23017 with a microcontroller at a different voltage level, ensure proper logic level shifting for the I2C lines.

#include <Wire.h>

// MCP23017 I2C address (configured by A0, A1 pins)
const int mcpAddress = 0x20;

// Registers addresses
const int IODIRA = 0x00; // I/O direction register for port A
const int IODIRB = 0x01; // I/O direction register for port B

void setup() {
  Wire.begin(); // Initialize I2C
  pinMode(13, OUTPUT); // Use onboard LED for output

  // Set all GPA pins to output, all GPB pins to input
  mcpWrite(IODIRA, 0x00); // All A pins as output
  mcpWrite(IODIRB, 0xFF); // All B pins as input
}

void loop() {
  // Toggle all GPA pins
  mcpWrite(0x12, 0xFF); // Turn on all GPA pins
  delay(500);
  mcpWrite(0x12, 0x00); // Turn off all GPA pins
  delay(500);
}

// Function to write data to a register on MCP23017
void mcpWrite(int reg, int data) {
  Wire.beginTransmission(mcpAddress);
  Wire.write(reg); // Register address
  Wire.write(data); // Data to write
  Wire.endTransmission();
}

• I2C Communication Failure: Ensure that the MCP23017 is powered correctly and that the SCL and SDA lines are connected properly with pull-up resistors.
• Incorrect Pin Behavior: Verify that the I/O pins have been configured correctly by writing to the IODIRA and IODIRB registers.
• Device Not Responding: Check the hardware address pins (A0, A1) and ensure they match the address used in the code.

• Use an I2C scanner sketch to confirm that the MCP23017 is detected on the I2C bus.
• Check for solder bridges or cold solder joints that might be causing shorts or open circuits.
• Ensure that the RESET pin is not inadvertently being pulled low during operation, which would reset the device.

Q: Can I use multiple MCP23017 devices on the same I2C bus? A: Yes, you can use up to 8 MCP23017 devices on the same I2C bus by configuring each with a unique hardware address (0x20-0x27).

Q: What is the maximum I2C clock frequency the MCP23017 can handle? A: The MCP23017 supports a maximum I2C clock frequency of 1.7 MHz in HS mode.

Q: Do I need to use external pull-up resistors on the I/O pins? A: No, external pull-up resistors are not required on the I/O pins unless you are using them in an open-drain configuration.