2020-05-11: v1.0.7 - Checked with architectures AVR, SAM and ESP32.
2020-05-02: v1.0.6 - void end() changed to bool end(). void wait() changed to bool wait().
2020-05-02: v1.0.5 - README.md updated. write(data, quantity) updated. New folder extras.
2019-01-08: v1.0.1 - Checked for ESP32.
2019-01-05: v1.0.0 - Initial commit.
- http://www.ti.com/lit/ml/scyb031/scyb031.pdf
- http://www.ti.com/lit/ds/symlink/pcf8574.pdf
- https://www.nxp.com/docs/en/data-sheet/PCF8574_PCF8574A.pdf
- The LCM2004A LCD module (HD44780U device) interfaced for I2C with a PCF8574.
The PCF8574 design is very simple: each pin of the eight P0..P7 could be an INPUT_PULLUP or a OPEN_DRAIN. A logical "1" sets the pin to high level through a low current pullup resistor, it's a INPUT_PULLUP input mode. A logical "0" sets the pin to low level through a low current open drain transistor, it's a OPEN_DRAIN output mode. To speed transition toward low level, the current is overloaded during the transition.
After device reset, all pins are set to logical "1" and operate as INPUT_PULLUP. There is no I2C command to reset the device else power down it.
begin()connects the device and end() or any I2C errors disconnect it. If device is disconnected, read() or write() fail immediately, the device needs to be reconnected. The connectedstatus is readable with bool()operator or connected()property.
class jm_PCF8574
{
public:
jm_PCF8574();
jm_PCF8574(uint8_t i2c_address);
operator bool();
uint8_t i2c_address();
bool connected();
bool begin();
bool begin(uint8_t i2c_address);
void end();
int read();
size_t write(uint8_t value);
size_t write(const uint8_t *data, size_t quantity);
void pinMode(uint8_t pin, uint8_t mode);
int digitalRead(uint8_t pin);
void digitalWrite(uint8_t pin, uint8_t value);
};
jm_PCF8574();
jm_PCF8574(uint8_t i2c_address);
operator bool();
uint8_t i2c_address();
bool connected();
The constructor can optionally set the i2c_address, or the i2c_address can be fixed later with begin().
The bool operator returns the connected status of the device, true if connected and not I2C errored, false else.
bool begin();
bool begin(uint8_t i2c_address);
void end();
begin()connects the device and checks the connectivity with it, returnstrueifconnected.end()disconnects the device.
int read();
size_t write(uint8_t value);
size_t write(const uint8_t *data, size_t quantity);
read()reads the eight Quasi-bidirectional I/Os P0..P7.write(value)writesvalueto the eight Quasi-bidirectional I/Os P0..P7.write(data, quantity)writesdatato the Quasi-bidirectional I/Os P0..P7. Eachdatais written atI2C speed(default speed 100 kbits/s).
void pinMode(uint8_t pin, uint8_t mode);
int digitalRead(uint8_t pin);
void digitalWrite(uint8_t pin, uint8_t value);
These methods reproduce the behaviors of Arduino digital pins. Pins are numbered 0..7.
pinMode(pin, mode)sets one bit of the Quasi-bidirectional I/Os P0..P7 as INPUT or OUTPUT. INPUT could be more understood as an INPUT_PULLUP and OUTPUT as a OPEN_DRAIN due to the PCF8574 design.digitalRead(pin)reads one of the eight Quasi-bidirectional I/Os P0..P7.digitalWrite(pin, value)writes one of the eight Quasi-bidirectional I/Os P0..P7.
- Blinking backlight of a LCD module.
This example blinks the backlight of a LCM2004A I2C LCD module.
The LCM2004A module is commonly interfaced for I2C with a PCF8574A or optionaly a PCF8574.
The default I2C address of the module is commonly 0x3F or optionaly 0x27.
The LCD display is driven by a Hitachi HD447800.
Common color of display is blue or optionaly yellow.
Common size is 20 columns by 4 rows.
- https://www.banggood.com/search/i2c-2004-204-20-x-4-character-lcd-display-module.html?from=nav
- https://ch.farnell.com/powertip/pc2004ars-awa-a-q/lcd-modul-stn-reflect-20x4/dp/1671507