PCF8574

Arduino library for PCF8574 - 8 channel I2C IO expander

Description

Related to the PCF8575 16 channel IO expander library https://github.com/RobTillaart/PCF8575

This library gives easy control over the 8 pins of a PCF8574 and PCF8574A chip. These chips are identical in behavior although there are two distinct address ranges.

TYPE	ADDRESS-RANGE	notes
PCF8574	0x20 to 0x27	same range as PCF8575 !!
PCF8574A	0x38 to 0x3F

So you can connect up to 16 PCF8574 on one I2C bus, giving access to 16 x 8 = 128 IO lines. To maximize IO lines combine 8 x PCF8575 + 8 x PCF8574A giving 128 + 64 = 192 IO lines. Be sure to have a well dimensioned power supply.

The library allows to read and write both single pins or 8 pins at once. Furthermore some additional functions are implemented that are playful but useful.

Interface

PCF8574_INITIAL_VALUE is a define that can be set compile time or before the include of "pcf8574.h" to overrule the default value used with the begin() call.

Constructor

PCF8574(deviceAddress, TwoWire *wire = &Wire) Constructor with device address, and optional the Wire interface as parameter.
bool begin(uint8_t val = PCF8574_INITIAL_VALUE) set the initial value for the pins and masks.
bool begin(uint8_t sda, uint8_t scl, uint8_t val = PCF8574_INITIAL_VALUE) idem, for the ESP32 where one can choose the I2C pins.
bool isConnected() checks if the address set in the constructor or by setAddress() is visible on the I2C bus.
bool setAddress(const uint8_t deviceAddress) sets the device address after construction. Can be used to switch between PCF8574 modules runtime. Note this corrupts internal buffered values, so one might need to call read8() and/or write8(). Returns true if address can be found on I2C bus.
uint8_t getAddress() returns the device address.

Read and Write

uint8_t read8() reads all 8 pins at once. This one does the actual reading.
uint8_t read(uint8_t pin) reads a single pin; pin = 0..7
uint8_t value() returns the last read inputs again, as this information is buffered in the class this is faster than reread the pins.
void write8(const uint8_t value) writes all 8 pins at once. This one does the actual reading.
uint8_t write(const uint8_t pin, const uint8_t value) writes a single pin; pin = 0..7; value is HIGH(1) or LOW (0)
valueOut() returns the last written data.

Button

void setButtonMask(const uint8_t mask)
uint8_t readButton8()
uint8_t readButton8(const uint8_t mask)
uint8_t readButton(const uint8_t pin)

Special

void toggle(const uint8_t pin) toggles a single pin
void toggleMask(const uint8_t mask = 0xFF) toggles a selection of pins, if you want to invert all pins use 0xFF (default value).
void shiftRight(const uint8_t n = 1) shifts output channels n pins (default 1) pins right (e.g. leds ). Fills the higher lines with zero's.
void shiftLeft(const uint8_t n = 1) shifts output channels n pins (default 1) pins left (e.g. leds ). Fills the lower lines with zero's.
void rotateRight(const uint8_t n = 1) rotates output channels to right, moving lowest line to highest line.
void rotateLeft(const uint8_t n = 1) rotates output channels to left, moving highest line to lowest line.
void reverse() reverse the "bit pattern" of the lines, high to low and vice versa.

Misc

int lastError() returns the last error from the lib. (see .h file)

Error codes

name	value	description
PCF8574_OK	0x00	no error
PCF8574_PIN_ERROR	0x81	pin number out of range
PCF8574_I2C_ERROR	0x82	I2C communication error

Operation

See examples

FishGPT / Arduino-PCF8574