Wiring the PCF8574AP 8bit Bidirectional IO Expander Driven i2C Communication Bus / SPI

This is the PCF8574AP consists of an 8-bit quasi-bidirectional port and an i2C Serial Bus Interface. The PCF8574AP has a low current consumption and includes latched output with HIGH consumption and include latched output with high current drive capability for directly driving LEDS. It also possesses an interrupt which can be connected to the interrupt logic of the Microcontroller, by sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via the i2C bus. This means that the PCF8574 can remain a simple slave device. This device is useful when you want to extend the IO pins of your Microcontroller using i2C Serial Communication Bus or SPI.

The Integrated PCF8574AP providing 8 ports INPUT / OUTPUT ports that can be manage using i2C serial communication. The following diagram below shows how to wire the PCF8574AP using OUTPUT series of LED served as indicator of our IO pins there are two diagram shows below one is the LED output and the tactile push button switch served as INPUT.

Required Component

Arduino Microcontroller, Teensy (TeensyDuino Integrated), ESP8266, STMXX
PCF8574AP Chip / PCF8574AP Board
Solder Less Bread Board
Jumper Wire

Wiring Guide

The first code below will test the circuit allow you to turn off and on a series of connected LED’s to IO ports.

Source Code for OUTPUT

#include <Wire.h>
int core = 1000;

void setup () 
{ 
Serial.begin(9600);
Serial.println("14CORE | PCF8574AP IO EXPANSION TEST CODE");
Serial.println("-----------------------------------------");
Serial.println("Begin...");
Wire.begin (); 
delay(core); 
}

void loop () 
{ 

Wire.beginTransmission (0x38); //Set P0 pin to logic level HIGH
Wire.write ((byte) 0b00000001); //Send byte to write 0b00000001
Wire.endTransmission(); //Set to end transmission
delay(core);

Wire.beginTransmission (0x38); //Start begin transmission to address 0x38 set PO logic level LOW
Wire.write((byte) 0b00000000);  //Send a byte.
Wire.endTransmission (); //End transmissions.
delay (core); 

Wire.beginTransmission (0x38);
Wire.write((byte) 0b11111111); //Set all pin P0, P1, P2, P3, P4, P5, P6, P7 to logic level HIGH
Wire.endTransmission ();
delay(core);

Wire.beginTransmission (0x38);
Wire.write((byte) 0b00000000); //Set all pin P0, P1, P2, P3, P4, P5, P6, P7 to logic level LOW
Wire.endTransmission ();
delay(core);
}

#include <Wire.h>

int core = 1000;

void setup ()

{

Serial.begin(9600);

Serial.println("14CORE | PCF8574AP IO EXPANSION TEST CODE");

Serial.println("-----------------------------------------");

Serial.println("Begin...");

Wire.begin ();

delay(core);

}

void loop ()

{

Wire.beginTransmission (0x38); //Set P0 pin to logic level HIGH

Wire.write ((byte) 0b00000001); //Send byte to write 0b00000001

Wire.endTransmission(); //Set to end transmission

delay(core);

Wire.beginTransmission (0x38); //Start begin transmission to address 0x38 set PO logic level LOW

Wire.write((byte) 0b00000000); //Send a byte.

Wire.endTransmission (); //End transmissions.

delay (core);

Wire.beginTransmission (0x38);

Wire.write((byte) 0b11111111); //Set all pin P0, P1, P2, P3, P4, P5, P6, P7 to logic level HIGH

Wire.endTransmission ();

delay(core);

Wire.beginTransmission (0x38);

Wire.write((byte) 0b00000000); //Set all pin P0, P1, P2, P3, P4, P5, P6, P7 to logic level LOW

Wire.endTransmission ();

delay(core);

}

Source Code for INPUT

#include <Wire.h>
int core1 = 6000;
int core2 = 1000;

void setup () 
{ 
Serial.begin (9600); 
Serial.println("14CORE | PCF8574AP IO EXPANSION FOR INPUT");
Serial.println("-----------------------------------------");
Serial.println("Begin...");
delay(core1);

Wire.begin (); 
delay(core2); 
}

void loop () 
{ 
Wire.requestFrom (0x38,1); 
if (Wire.available ()) 
{ 
Serial.print("IO : "); 
Serial.print(Wire.read (), BIN); 
}
delay (core2); 
}

#include <Wire.h>

int core1 = 6000;

int core2 = 1000;

void setup ()

{

Serial.begin (9600);

Serial.println("14CORE | PCF8574AP IO EXPANSION FOR INPUT");

Serial.println("-----------------------------------------");

Serial.println("Begin...");

delay(core1);

Wire.begin ();

delay(core2);

}

void loop ()

{

Wire.requestFrom (0x38,1);

if (Wire.available ())

{

Serial.print("IO : ");

Serial.print(Wire.read (), BIN);

}

delay (core2);

}

Downloads

Download PCF8574AP Datasheet | PDF

Wiring the PCF8574AP 8bit Bidirectional IO Expander Driven i2C Communication Bus / SPI

Tagged on: i2c IO Microcontroller Serial SPI

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