The PCF8574 is an 8 bits I/O port expander that uses the I2C protocol. Using this IC, you can use only the SDA and SCL pins of your Arduino board to control up to 8 digital I/O ports.
A0,A1,A2 are address pins
P0,P1,P2,P3,P4,P5,P6,P7 are digital I/O ports
SDA,SCL are the I2C pins
If we set pins A0 to A2 to GND, our device address in binary will be 0x20, thats exactly what I did in my example. To enable read and write there are different values required you can see these in the image below
Schematic
Note that the PCF8574 is a current sink device so you do not require the current limiting resistors
I have only shown 2 LEDs, also note that I have shown A0, A1 and A2 tied to GND, this is what my test module had selected.
microbit and pcf8574
Code
This example flashes the led’s
[codesyntax lang=”cpp”]
#include <Wire.h>
// address of PCF8574 IC
#define PCF8574_ADDR (0x20)
void setup()
{
Wire.begin();
}
void loop()
{
//send the data
Wire.beginTransmission(PCF8574_ADDR);
Wire.write(0xAA);
Wire.endTransmission();
delay(1000);
Wire.beginTransmission(PCF8574_ADDR);
Wire.write(0x55);
Wire.endTransmission();
delay(1000);
}
[/codesyntax]
Link