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# zh_pcf8574 - PCF8574(A) 8-bit I/O Expander Component for ESP-IDF
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## Table of Contents
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- [Overview](#overview)
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- [Features](#features)
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- [Installation](#installation)
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- [API Reference](#api-reference)
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- [Usage Examples](#usage-examples)
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- [Technical Specifications](#technical-specifications)
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- [Error Codes](#error-codes)
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- [Contributing](#contributing)
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- [License](#license)
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---
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## Overview
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`zh_pcf8574` is an ESP-IDF component for 8-bit I/O expanders PCF8574 and PCF8574A. It provides a convenient API for working with GPIO expanders via I2C bus. The component supports up to 16 expanders on a single I2C bus and can generate interrupts when input GPIO states change.
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The component is designed specifically for ESP32 microcontrollers and uses ESP-IDF v5.0+ I2C driver API.
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---
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## Features
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1. **Support for 16 Expanders**: Up to 16 PCF8574(A) on one I2C bus (addresses 0x20-0x27 and 0x38-0x3F)
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2. **GPIO Modes**: Support for output and input modes for each of the 8 GPIO pins
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3. **Interrupt Generation**: Support for interrupts from input GPIOs (negative edge)
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4. **Error Statistics**: Built-in counters for I2C, event, vector, and queue overflow errors
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5. **Thread-Safe**: Uses ESP-IDF I2C driver and FreeRTOS
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6. **Minimal Overhead**: Low memory and CPU requirements
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7. **Simple API**: Easy read/write for all GPIO and individual pins
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---
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## Installation
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1. Navigate to your project's components directory:
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```bash
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cd ../your_project/components
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```
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2. Clone the repository:
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```bash
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git clone https://github.com/aZholtikov/zh_pcf8574.git
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```
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3. In your application, include the header:
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```c
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#include "zh_pcf8574.h"
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```
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4. The component will be automatically built with your project.
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### Required menuconfig Settings
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For correct operation, enable the following settings in menuconfig:
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```text
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GPIO_CTRL_FUNC_IN_IRAM
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I2C_ISR_IRAM_SAFE
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I2C_MASTER_ISR_HANDLER_IN_IRAM
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```
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---
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## API Reference
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### Macros
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```c
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#define ZH_PCF8574_GPIO_OUTPUT false
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#define ZH_PCF8574_GPIO_INPUT true
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#define ZH_PCF8574_GPIO_LOW false
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#define ZH_PCF8574_GPIO_HIGH true
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```
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---
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### zh_pcf8574_init_config_t Structure
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```c
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typedef struct
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{
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i2c_master_bus_handle_t i2c_handle; // Unique I2C bus handle
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uint32_t i2c_frequency; // I2C frequency of the expander (max 100000 Hz)
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uint16_t stack_size; // Stack size for interrupt processing task
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uint8_t task_priority; // Priority of interrupt processing task
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uint8_t i2c_address; // I2C address of the expander (0x20-0x27 or 0x38-0x3F)
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bool p0_gpio_work_mode; // GPIO P0 work mode (false - output, true - input)
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bool p1_gpio_work_mode; // GPIO P1 work mode
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bool p2_gpio_work_mode; // GPIO P2 work mode
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bool p3_gpio_work_mode; // GPIO P3 work mode
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bool p4_gpio_work_mode; // GPIO P4 work mode
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bool p5_gpio_work_mode; // GPIO P5 work mode
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bool p6_gpio_work_mode; // GPIO P6 work mode
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bool p7_gpio_work_mode; // GPIO P7 work mode
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gpio_num_t interrupt_gpio; // Interrupt GPIO (GPIO_NUM_MAX - disable)
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} zh_pcf8574_init_config_t;
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```
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Use `ZH_PCF8574_INIT_CONFIG_DEFAULT()` macro to initialize with default values:
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- `i2c_frequency`: 100000 Hz
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- `i2c_address`: 0xFF
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- `p0_gpio_work_mode` ... `p7_gpio_work_mode`: `ZH_PCF8574_GPIO_OUTPUT`
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- `interrupt_gpio`: `GPIO_NUM_MAX`
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---
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### zh_pcf8574_handle_t Structure
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```c
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typedef struct
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{
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uint8_t i2c_address; // I2C address of the expander
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uint8_t gpio_work_mode; // GPIO work modes (bits 0-7)
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uint8_t gpio_status; // Current GPIO status (bits 0-7)
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bool is_initialized; // Expander initialization flag
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i2c_master_dev_handle_t dev_handle; // Unique I2C device handle
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void *system; // System pointer for use in other components
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} zh_pcf8574_handle_t;
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```
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---
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### zh_pcf8574_stats_t Structure
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```c
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typedef struct
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{
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uint32_t i2c_driver_error; // Number of I2C driver errors
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uint32_t event_post_error; // Number of event post errors
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uint32_t vector_error; // Number of vector errors
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uint32_t queue_overflow_error; // Number of queue overflow errors
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uint32_t min_stack_size; // Minimum free stack of the task
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} zh_pcf8574_stats_t;
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```
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---
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### zh_pcf8574_event_on_isr_t Structure
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```c
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typedef struct
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{
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uint64_t interrupt_time; // Interrupt time (microseconds)
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zh_pcf8574_gpio_num_t gpio_number; // GPIO number that caused the interrupt
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uint8_t i2c_address; // I2C address of the expander
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bool gpio_level; // GPIO level at interrupt time
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} zh_pcf8574_event_on_isr_t;
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```
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---
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### zh_pcf8574_init()
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Initializes the PCF8574 expander.
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**Parameters:**
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- `config` - Pointer to PCF8574 initialization configuration structure
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- `handle` - Pointer to unique PCF8574 handle
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument (NULL config or handle)
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- `ESP_ERR_INVALID_STATE` - Expander already initialized
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- `ESP_FAIL` - Initialization failed
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---
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### zh_pcf8574_deinit()
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Deinitializes the PCF8574 expander.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument (NULL handle)
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- `ESP_ERR_INVALID_STATE` - Expander not initialized
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- `ESP_FAIL` - Deinitialization failed
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---
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### zh_pcf8574_read()
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Reads the state of all GPIO pins of the expander.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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- `reg` - Pointer to store GPIO status (bits 0-7)
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument (NULL handle or reg)
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- `ESP_ERR_NOT_FOUND` - Expander not initialized
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- `ESP_FAIL` - I2C communication error
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**Note:** For input GPIOs, the value will always be 1 (HIGH).
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---
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### zh_pcf8574_write()
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Sets the state of all output GPIO pins of the expander.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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- `reg` - GPIO status (bits 0-7)
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument (NULL handle)
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- `ESP_ERR_NOT_FOUND` - Expander not initialized
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- `ESP_FAIL` - I2C communication error
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**Note:** Only output GPIOs are affected.
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---
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### zh_pcf8574_reset()
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Resets all GPIO pins of the expander to the initial state.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument (NULL handle)
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- `ESP_ERR_NOT_FOUND` - Expander not initialized
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- `ESP_FAIL` - I2C communication error
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---
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### zh_pcf8574_read_gpio()
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Reads the state of one GPIO pin of the expander.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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- `gpio` - GPIO number (ZH_PCF8574_GPIO_NUM_P0 ... ZH_PCF8574_GPIO_NUM_P7)
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- `status` - Pointer to store GPIO status (true - HIGH, false - LOW)
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument
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- `ESP_ERR_NOT_FOUND` - Expander not initialized
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- `ESP_FAIL` - I2C communication error
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**Note:** For input GPIOs, the value will always be 1 (HIGH).
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---
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### zh_pcf8574_write_gpio()
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Sets the state of one output GPIO pin of the expander.
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**Parameters:**
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- `handle` - Pointer to unique PCF8574 handle
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- `gpio` - GPIO number (ZH_PCF8574_GPIO_NUM_P0 ... ZH_PCF8574_GPIO_NUM_P7)
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- `status` - GPIO status (true - HIGH, false - LOW)
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**Returns:**
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- `ESP_OK` - Success
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- `ESP_ERR_INVALID_ARG` - Invalid argument
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- `ESP_ERR_NOT_FOUND` - Expander not initialized
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- `ESP_FAIL` - I2C communication error
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**Note:** Only output GPIOs are affected.
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---
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### zh_pcf8574_get_stats()
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Gets error statistics since last reset.
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**Returns:**
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- Pointer to the statistics structure
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**Example:**
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```c
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const zh_pcf8574_stats_t *stats = zh_pcf8574_get_stats();
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printf("I2C errors: %ld\n", stats->i2c_driver_error);
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```
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---
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### zh_pcf8574_reset_stats()
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Resets error statistics counters.
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**Example:**
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```c
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zh_pcf8574_reset_stats();
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```
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---
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## Usage Examples
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### Basic Example: Single Expander
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```c
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#include "zh_pcf8574.h"
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#define I2C_PORT (I2C_NUM_MAX - 1)
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zh_pcf8574_handle_t pcf8574_handle = {0};
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void print_gpio_status(const char *message, uint8_t reg)
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{
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printf("%s", message);
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for (uint8_t i = 0; i < 8; ++i)
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{
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printf("%c", (reg & 0x80) ? '1' : '0');
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reg <<= 1;
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}
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printf(".\n");
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}
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void app_main(void)
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{
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esp_log_level_set("zh_pcf8574", ESP_LOG_ERROR);
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i2c_master_bus_config_t i2c_bus_config = {
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.clk_source = I2C_CLK_SRC_DEFAULT,
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.i2c_port = I2C_PORT,
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.scl_io_num = GPIO_NUM_22,
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.sda_io_num = GPIO_NUM_21,
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.glitch_ignore_cnt = 7,
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.flags.enable_internal_pullup = true,
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};
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i2c_master_bus_handle_t i2c_bus_handle = NULL;
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i2c_new_master_bus(&i2c_bus_config, &i2c_bus_handle);
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zh_pcf8574_init_config_t config = ZH_PCF8574_INIT_CONFIG_DEFAULT();
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config.i2c_handle = i2c_bus_handle;
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config.i2c_address = 0x38;
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config.p0_gpio_work_mode = ZH_PCF8574_GPIO_INPUT; // P0 - input
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zh_pcf8574_init(&config, &pcf8574_handle);
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uint8_t reg = 0;
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zh_pcf8574_read(&pcf8574_handle, ®);
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print_gpio_status("GPIO status: ", reg);
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printf("Set P7 to 1, P1 to 1 and P0 to 0.\n");
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zh_pcf8574_write(&pcf8574_handle, 0b10000010);
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zh_pcf8574_read(&pcf8574_handle, ®);
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print_gpio_status("GPIO status: ", reg);
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printf("Set P0 to 0.\n");
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zh_pcf8574_write_gpio(&pcf8574_handle, ZH_PCF8574_GPIO_NUM_P0, ZH_PCF8574_GPIO_LOW);
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bool gpio = 0;
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zh_pcf8574_read_gpio(&pcf8574_handle, ZH_PCF8574_GPIO_NUM_P0, &gpio);
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printf("P0 status: %d.\n", gpio);
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printf("Set P1 to 0.\n");
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zh_pcf8574_write_gpio(&pcf8574_handle, ZH_PCF8574_GPIO_NUM_P1, ZH_PCF8574_GPIO_LOW);
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zh_pcf8574_read_gpio(&pcf8574_handle, ZH_PCF8574_GPIO_NUM_P1, &gpio);
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printf("P1 status: %d.\n", gpio);
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zh_pcf8574_read(&pcf8574_handle, ®);
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print_gpio_status("GPIO status: ", reg);
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printf("Reset all GPIO.\n");
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zh_pcf8574_reset(&pcf8574_handle);
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zh_pcf8574_read(&pcf8574_handle, ®);
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print_gpio_status("GPIO status: ", reg);
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const zh_pcf8574_stats_t *stats = zh_pcf8574_get_stats();
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printf("I2C errors: %ld.\n", stats->i2c_driver_error);
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}
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```
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---
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### Example with Interrupts
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```c
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#include "zh_pcf8574.h"
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#define I2C_PORT (I2C_NUM_MAX - 1)
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zh_pcf8574_handle_t pcf8574_handle = {0};
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void zh_pcf8574_event_handler(void *arg, esp_event_base_t event_base, int32_t event_id, void *event_data)
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{
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zh_pcf8574_event_on_isr_t *event = event_data;
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printf("Interrupt on device 0x%02X, GPIO %d, level %d, time %lld.\n",
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event->i2c_address, event->gpio_number, event->gpio_level, event->interrupt_time);
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}
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void app_main(void)
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{
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esp_log_level_set("zh_pcf8574", ESP_LOG_ERROR);
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i2c_master_bus_config_t i2c_bus_config = {
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.clk_source = I2C_CLK_SRC_DEFAULT,
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.i2c_port = I2C_PORT,
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.scl_io_num = GPIO_NUM_22,
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.sda_io_num = GPIO_NUM_21,
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.glitch_ignore_cnt = 7,
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.flags.enable_internal_pullup = true,
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};
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i2c_master_bus_handle_t i2c_bus_handle = NULL;
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i2c_new_master_bus(&i2c_bus_config, &i2c_bus_handle);
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esp_event_loop_create_default();
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esp_event_handler_instance_register(ZH_PCF8574, ESP_EVENT_ANY_ID, &zh_pcf8574_event_handler, NULL, NULL);
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zh_pcf8574_init_config_t config = ZH_PCF8574_INIT_CONFIG_DEFAULT();
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config.i2c_handle = i2c_bus_handle;
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config.i2c_address = 0x38;
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config.p0_gpio_work_mode = ZH_PCF8574_GPIO_INPUT; // P0 - input for interrupts
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config.interrupt_gpio = GPIO_NUM_14; // Connect INT to GPIO 14
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zh_pcf8574_init(&config, &pcf8574_handle);
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for (;;)
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{
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const zh_pcf8574_stats_t *stats = zh_pcf8574_get_stats();
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printf("I2C errors: %ld.\n", stats->i2c_driver_error);
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printf("Event errors: %ld.\n", stats->event_post_error);
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printf("Interrupt queue: %ld.\n", stats->queue_overflow_error);
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printf("Minimum free stack: %ld.\n", stats->min_stack_size);
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vTaskDelay(60000 / portTICK_PERIOD_MS);
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}
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}
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```
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||||
---
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||||
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||||
## Technical Specifications
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||||
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||||
| Parameter | Value |
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||||
|-----------|-------|
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||||
| **Device Type** | 8-bit I2C GPIO expander |
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||||
| **Models** | PCF8574, PCF8574A |
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||||
| **Number of devices on bus** | Up to 16 (addresses 0x20-0x27, 0x38-0x3F) |
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||||
| **Number of GPIO** | 8 (P0-P7) |
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||||
| **I2C Address** | 0x20-0x27 (PCF8574), 0x38-0x3F (PCF8574A) |
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||||
| **I2C Frequency** | Up to 100 kHz |
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| **GPIO Modes** | Input/Output (configurable per pin) |
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||||
| **Interrupts** | Yes (negative edge) |
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||||
| **ESP-IDF Version** | >= 5.0 |
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||||
| **Platform** | ESP32 series |
|
||||
| **Language** | C (C99) |
|
||||
|
||||
---
|
||||
|
||||
## Error Codes
|
||||
|
||||
| Error Code | Description |
|
||||
|------------|-------------|
|
||||
| `ESP_OK` | Operation successful |
|
||||
| `ESP_ERR_INVALID_ARG` | Invalid argument (NULL pointer or invalid configuration) |
|
||||
| `ESP_ERR_INVALID_STATE` | Device not initialized or already initialized |
|
||||
| `ESP_ERR_NOT_FOUND` | Device not initialized |
|
||||
| `ESP_ERR_NO_MEM` | Insufficient memory |
|
||||
| `ESP_FAIL` | General failure (I2C communication error, initialization error, etc.) |
|
||||
|
||||
---
|
||||
|
||||
## Contributing
|
||||
|
||||
Contributions are welcome! To contribute:
|
||||
|
||||
1. Fork the repository
|
||||
2. Create a feature branch (`git checkout -b feature/AmazingFeature`)
|
||||
3. Commit your changes (`git commit -m 'Add some AmazingFeature'`)
|
||||
4. Push to the branch (`git push origin feature/AmazingFeature`)
|
||||
5. Open a Pull Request
|
||||
|
||||
Please ensure your code follows the existing style and includes appropriate documentation.
|
||||
|
||||
---
|
||||
|
||||
## License
|
||||
|
||||
This project is licensed under the Apache License, Version 2.0 - see the [LICENSE](LICENSE) file for details.
|
||||
|
||||
### Apache License, Version 2.0
|
||||
|
||||
Copyright (c) 2026 Alexey Zholtikov
|
||||
|
||||
Licensed under the Apache License, Version 2.0 (the "License");
|
||||
you may not use this file except in compliance with the License.
|
||||
You may obtain a copy of the License at
|
||||
|
||||
http://www.apache.org/licenses/LICENSE-2.0
|
||||
|
||||
Unless required by applicable law or agreed to in writing, software
|
||||
distributed under the License is distributed on an "AS IS" BASIS,
|
||||
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||||
See the License for the specific language governing permissions and
|
||||
limitations under the License.
|
||||
|
||||
---
|
||||
|
||||
## Additional Notes
|
||||
|
||||
- **I2C Pull-up Resistors**: Ensure pull-up resistors are connected to SDA and SCL lines (typically 4.7kΩ)
|
||||
- **Input GPIOs**: All input GPIOs are internally pulled up to VCC (~100kΩ resistor)
|
||||
- **Interrupts**: All INT outputs of expanders must be connected to one GPIO on ESP32
|
||||
- **I2C_ISR_IRAM_SAFE**: For correct operation, enable `I2C_ISR_IRAM_SAFE` and `I2C_MASTER_ISR_HANDLER_IN_IRAM` in menuconfig
|
||||
- **GPIO_CTRL_FUNC_IN_IRAM**: For GPIO interrupts, enable `GPIO_CTRL_FUNC_IN_IRAM` in menuconfig
|
||||
|
||||
---
|
||||
|
||||
*Generated for zh_pcf8574 v2.8.1*
|
||||
Reference in new issue
Block a user