#include "Wire.h"

void setup()
{
  Serial.begin (115200);
  Wire.begin(); // wake up I2C bus
  Wire.beginTransmission(0x20);
  Wire.write(0x00); // IODIRA register
  Wire.write(0x00); // set all of bank A to outputs
  Wire.endTransmission();
}
void loop()   
{
  Wire.beginTransmission(0x20);
  Wire.write(0x12); // memory pointer to DATA BANK A
  Wire.write(0xFF); // WRITE ALL  ON
  Wire.endTransmission();
  delay(1000);
}