How to Use TCA9535: Examples, Pinouts, and Specs

The TCA9535 is a 16-bit I2C I/O port expander manufactured by MEOW. It is designed to expand the number of GPIO pins available in microcontroller-based applications. The device communicates via the I2C protocol, making it easy to integrate into systems with limited GPIO resources. The TCA9535 features two 8-bit ports, interrupt capabilities, and supports multiple devices on the same I2C bus through configurable I2C addresses.

• Expanding GPIO pins in microcontroller projects
• Driving LEDs, relays, or other digital outputs
• Reading multiple digital inputs such as switches or sensors
• Applications requiring interrupt-driven GPIO monitoring
• I2C-based systems with limited GPIO availability

The following table outlines the key technical details of the TCA9535:

The TCA9535 is available in a 24-pin package. Below is the pin configuration and description:

1. Power Supply: Connect the Vcc pin to a voltage source between 1.65V and 5.5V. Connect the GND pin to the ground of the circuit.
2. I2C Address Configuration: Use the A0, A1, and A2 pins to set the I2C address. These pins can be tied to Vcc or GND to configure the address.
3. I2C Communication: Connect the SDA and SCL pins to the corresponding I2C lines of the microcontroller. Use pull-up resistors (typically 4.7kΩ) on both lines.
4. GPIO Usage: Use the P0_x and P1_x pins as general-purpose input or output pins. Configure their direction and state via I2C commands.
5. Interrupt Handling: If using interrupts, connect the INT pin to a microcontroller GPIO pin configured as an interrupt input.

• Ensure proper pull-up resistors are used on the I2C lines (SDA and SCL).
• Avoid exceeding the maximum current sink capability (25 mA per pin).
• Use decoupling capacitors (e.g., 0.1 µF) near the Vcc pin to stabilize the power supply.
• If unused, tie the RESET pin to Vcc to prevent accidental resets.
• Handle the INT pin carefully as it is open-drain and requires a pull-up resistor.

Below is an example of how to use the TCA9535 with an Arduino UNO to toggle GPIO pins:

#include <Wire.h> // Include the Wire library for I2C communication

#define TCA9535_ADDR 0x20 // Default I2C address (adjust based on A0, A1, A2)

// TCA9535 Register Addresses
#define INPUT_PORT_0  0x00
#define INPUT_PORT_1  0x01
#define OUTPUT_PORT_0 0x02
#define OUTPUT_PORT_1 0x03
#define CONFIG_PORT_0 0x06
#define CONFIG_PORT_1 0x07

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Configure all pins on Port 0 as outputs
  Wire.beginTransmission(TCA9535_ADDR);
  Wire.write(CONFIG_PORT_0); // Point to configuration register for Port 0
  Wire.write(0x00); // Set all pins as outputs (0 = output, 1 = input)
  Wire.endTransmission();

  // Set all pins on Port 0 to LOW
  Wire.beginTransmission(TCA9535_ADDR);
  Wire.write(OUTPUT_PORT_0); // Point to output register for Port 0
  Wire.write(0x00); // Set all pins to LOW
  Wire.endTransmission();
}

void loop() {
  // Toggle all pins on Port 0
  Wire.beginTransmission(TCA9535_ADDR);
  Wire.write(OUTPUT_PORT_0); // Point to output register for Port 0
  Wire.write(0xFF); // Set all pins to HIGH
  Wire.endTransmission();
  delay(1000); // Wait for 1 second

  Wire.beginTransmission(TCA9535_ADDR);
  Wire.write(OUTPUT_PORT_0); // Point to output register for Port 0
  Wire.write(0x00); // Set all pins to LOW
  Wire.endTransmission();
  delay(1000); // Wait for 1 second
}

1. I2C Communication Failure:

   • Cause: Incorrect I2C address or missing pull-up resistors.
   • Solution: Verify the I2C address configuration (A0, A1, A2 pins) and ensure pull-up resistors are connected to SDA and SCL lines.

2. GPIO Pins Not Responding:

   • Cause: Incorrect configuration of GPIO direction.
   • Solution: Ensure the GPIO pins are configured as outputs or inputs as required using the configuration registers.

3. Interrupt Pin Not Working:

   • Cause: Missing pull-up resistor on the INT pin.
   • Solution: Add a pull-up resistor (e.g., 10kΩ) to the INT pin.

4. Overheating or Damage:

   • Cause: Exceeding the maximum current sink capability of GPIO pins.
   • Solution: Limit the current through each GPIO pin to 25 mA or less.

Q: Can the TCA9535 operate at 3.3V?
A: Yes, the TCA9535 supports a supply voltage range of 1.65V to 5.5V, making it compatible with 3.3V systems.

Q: How many TCA9535 devices can be connected to the same I2C bus?
A: Up to 8 devices can be connected by configuring the A0, A1, and A2 address pins.

Q: Is the TCA9535 compatible with 5V logic?
A: Yes, the TCA9535 can operate with 5V logic as long as the supply voltage (Vcc) is within the 1.65V to 5.5V range.

Q: What happens if the RESET pin is left floating?
A: The RESET pin should not be left floating. Tie it to Vcc if not used to prevent accidental resets.