Table of Contents

Pca95x4/PCA9534/PCA9534A/PCA9554/PCA9554A - I2C GPIO Expander

The PCA95x4 provides 8 bits of General Purpose parallel Input/Output (GPIO) expansion for I2C-bus applications.

Documentation

  • Philips I2C IO expanders application notes can be found here

NXP

Texas Instruments

Board

Connection Diagram

Usage

Important: make sure you properly setup the I2C pins especially for ESP32 before creating the I2cDevice, make sure you install the nanoFramework.Hardware.ESP32 nuget:

//////////////////////////////////////////////////////////////////////
// when connecting to an ESP32 device, need to configure the I2C GPIOs
// used for the bus
Configuration.SetPinFunction(21, DeviceFunction.I2C1_DATA);
Configuration.SetPinFunction(22, DeviceFunction.I2C1_CLOCK);

For other devices like STM32, please make sure you're using the preset pins for the I2C bus you want to use.

This example shows how to write value out to 8 LEDs using a PCA95x4 device and a MCU.

I2cConnectionSettings i2cConnectionSettings = new(1, 0x38);
I2cDevice i2cDevice = I2cDevice.Create(i2cConnectionSettings);
pca95x4 = new Pca95x4(i2cDevice);

Cycle output bits

pca95x4.Write(Register.Configuration, 0x00);  // Make all outputs.
pca95x4.Write(Register.OutputPort, 0xFF);  // Set all outputs.

for (int bitNumber = 0; bitNumber < 8; bitNumber++)
{
    pca95x4.WriteBit(Register.OutputPort, bitNumber, false);  // Clear output.
    Thread.Sleep(500);
    pca95x4.WriteBit(Register.OutputPort, bitNumber, true);  // Set output.
}

Read Input Port

pca95x4.Write(Register.Configuration, 0xFF);  // Make all inputs.
byte data = pca95x4.Read(Register.InputPort);
Debug.WriteLine($"Input Port: 0x{data:X2}");

Check Input Register Polarity Inversion

pca95x4.Write(Register.Configuration, 0xFF);  // Make all inputs.
byte data = pca95x4.Read(Register.InputPort);
Debug.WriteLine($"Input Register: 0x{data:X2}");
pca95x4.InvertInputRegisterPolarity(true);
data = pca95x4.Read(Register.InputPort);
Debug.WriteLine($"Input Register Polarity Inverted: 0x{data:X2}");
pca95x4.InvertInputRegisterPolarity(false);
data = pca95x4.Read(Register.InputPort);
Debug.WriteLine($"Input Register: 0x{data:X2}");

Binding Notes

PCA9534/PCA9554 and PCA9534A/PCA9554A are identical except for a few differences.

  • The removal of the internal I/O pull-up resistor which greatly reduces power consumption when the I/Os are held LOW.
  • Each has a fixed I2C address. This allows for up to 16 of these devices (8 of each) on the same I2C bus.
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