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mongoose-os-libs/pcf857x-i2c mgos_pcf857x.h    

A Mongoose library for PCF857X, a popular and cheap set of GPIO extenders using I2C. The PCF8574 is an 8-port device, and the PCF8575 is a 16-port device, but they are otherwise identical.

Implementation details

The PCF857X is a pseudo bi-directional GPIO, which means that by default ports are input and output. Writes to the ports can change the state from high to low. If the port is high, it is pulled up by a weak current. Each port can be pulled low by an external device, in which case reads from that port return 0. The implication is that "input" ports are always pulled high.

API Description

To start, mgos_pcf857x_create() is called with the correct I2C bus and address (by default 0x20), and optionally a GPIO pin on the microcontroller that serves as an interrupt pin, to detect PCF857X input state changes.

NOTE: When the driver starts, it polls the current state from the chip without changing any ports. The benefit of this is that the MCU can safely reboot without loss of the GPIO state in PCF857X.

The API follows mgos_gpio.h closely, enabling ports to be set as input (ignoring the pull_type, which is always pullup), or as output. Notably, mgos_pcf857x_gpio_set_int_handler() and mgos_pcf857x_gpio_set_button_handler() work identically to the mgos_gpio_*() variants.

Example application

#include "mgos.h"
#include "mgos_config.h"
#include "mgos_pcf857x.h"

static void button_cb(int pin, void *user_data) {
  struct mgos_pcf857x *d = (struct mgos_pcf857x *)user_data;
  LOG(LL_INFO, ("GPIO[%d] callback, value=%d", pin, mgos_pcf857x_gpio_read(d, pin)));
  mgos_pcf857x_gpio_toggle(d, pin+4);

enum mgos_app_init_result mgos_app_init(void) {
  struct mgos_pcf857x *d;
  int i;

  if (!(d = mgos_pcf8574_create(mgos_i2c_get_global(), mgos_sys_config_get_pcf857x_i2caddr(),
                                mgos_sys_config_get_pcf857x_int_gpio()))) {
    LOG(LL_ERROR, ("Could not create PCF857X"));

  for(i=0; i<4; i++) mgos_pcf857x_gpio_setup_input(d, i, MGOS_GPIO_PULL_UP);
  for(i=4; i<8; i++) mgos_pcf857x_gpio_set_mode(d, i, MGOS_GPIO_MODE_OUTPUT);

  mgos_pcf857x_gpio_set_button_handler(d, 0, MGOS_GPIO_PULL_UP, MGOS_GPIO_INT_EDGE_NEG, 10, button_cb, d);
  mgos_pcf857x_gpio_set_button_handler(d, 1, MGOS_GPIO_PULL_UP, MGOS_GPIO_INT_EDGE_POS, 10, button_cb, d);
  mgos_pcf857x_gpio_set_button_handler(d, 2, MGOS_GPIO_PULL_UP, MGOS_GPIO_INT_EDGE_ANY, 10, button_cb, d);
  mgos_pcf857x_gpio_set_button_handler(d, 3, MGOS_GPIO_PULL_UP, MGOS_GPIO_INT_EDGE_ANY, 10, button_cb, d);



This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.


struct mgos_pcf857x *mgos_pcf8574_create(struct mgos_i2c *i2c, uint8_t i2caddr, int int_gpio);
struct mgos_pcf857x *mgos_pcf8575_create(struct mgos_i2c *i2c, uint8_t i2caddr, int int_gpio);

Initialize a PCF857X on the I2C bus i2c at address specified in i2caddr parameter (default PCF857X is on address 0x20). The device will be polled for validity, upon success a new struct mgos_pcf857x is allocated and returned. If the device could not be found, NULL is returned. To install an interrupt handler for the chip, set int_gpio to any valid GPIO pin. Set it to -1 to disable interrupts.


bool mgos_pcf857x_destroy(struct mgos_pcf857x **dev);

Destroy the data structure associated with a PCF857X device. The reference to the pointer of the struct mgos_pcf857x has to be provided, and upon successful destruction, its associated memory will be freed and the pointer set to NULL and true will be returned.


void mgos_pcf857x_print_state(struct mgos_pcf857x *dev);

Emit a logline with the pin and io register stat


bool mgos_pcf857x_gpio_set_mode(struct mgos_pcf857x *dev, int pin, enum mgos_gpio_mode mode);
bool mgos_pcf857x_gpio_setup_output(struct mgos_pcf857x *dev, int pin, bool level);
bool mgos_pcf857x_gpio_setup_input(struct mgos_pcf857x *dev, int pin, enum mgos_gpio_pull_type pull_type);
bool mgos_pcf857x_gpio_read(struct mgos_pcf857x *dev, int pin);
void mgos_pcf857x_gpio_write(struct mgos_pcf857x *dev, int pin, bool level);
bool mgos_pcf857x_gpio_toggle(struct mgos_pcf857x *dev, int pin);

These follow mgos_gpio.h definitions.

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