/*

http://www.bristolwatch.com/arduino/arduino6c.htm
PCA9555 32-Bit GPIO Expander with Arduino Using Interrupts
Lewis Loflin lewis@bvu.net

*/



#include <Wire.h> // specify use of Wire.h library.

int i, j;
byte temp1;

volatile byte flag_bit = LOW;

void setup()

{
  pinMode(2, INPUT);
  Wire.begin();
  Wire.beginTransmission(0x20);  // setup out direction registers
  Wire.write(0x06);  // pointer
  Wire.write(0x0F);  // DDR Port0 bits 0-3 input 4-7 output 
  Wire.write(0x00);  // DDR Port1 all output
  Wire.endTransmission(); 

  Wire.beginTransmission(0x20);  // 
  Wire.write(0x02);  // pointer
  Wire.write(0x00);  // clear bits 4-7 PORT0
  Wire.endTransmission(); 

  Wire.beginTransmission(0x20);  // invert bit
  Wire.write(0x04);  // pointer
  Wire.write(0xFF);  // invert bits PORT0 on read
  Wire.endTransmission(); 
  
    // clear LEDs PORT1
  Wire.beginTransmission(0x20);  
  Wire.write(0x03); // begin here
  Wire.write(temp1); 
  Wire.endTransmission();
  
  
  attachInterrupt(0, flag1, FALLING); 
}  // end setup

void loop() {

  if (flag_bit = HIGH)  {
    detachInterrupt(0); 
    temp1 = getKey(); // scan keypad for BCD code. 
    if (temp1 != 0x00)   {
      Wire.beginTransmission(0x20);  
      Wire.write(0x03); // begin here
      Wire.write(temp1); 
      Wire.endTransmission();
    }

    flag_bit = 0x00;
    attachInterrupt(0, flag1, FALLING); 

  }





} // end loop


void flag1() // set bit
{
  flag_bit = HIGH; 
} 




byte getKey()  {



  Wire.beginTransmission(0x20);  
  Wire.write(0);  // set data pointer
  Wire.endTransmission();
  Wire.requestFrom(0x20, 1);
  byte c = Wire.read();
  if ((c & 0x0F) == 0) return 0x00;  // no key pressed


  Wire.beginTransmission(0x20);
  Wire.write(0x02);
  Wire.write(B11100000); // check row L1
  Wire.endTransmission();

  Wire.beginTransmission(0x20);  
  Wire.write(0);  // set data pointer
  Wire.endTransmission();
  Wire.requestFrom(0x20, 1);
  c = Wire.read();
  if ((c & 0x1F) > 0x10) {
    if (c==B00010001) c = 0x01; 
    if (c==B00010010) c = 0x02; 
    if (c==B00010100) c = 0x03; 
    if (c==B00011000) c = 0x04;
    delay(100);
    resetPort0();
    return c;
  }

  Wire.beginTransmission(0x20);
  Wire.write(0x02);
  Wire.write(B11010000); // check row L2
  Wire.endTransmission(); 

  Wire.beginTransmission(0x20);  
  Wire.write(0);  // set data pointer
  Wire.endTransmission();
  Wire.requestFrom(0x20, 1);
  c = Wire.read();
  if ((c & 0x2F) > 0x20) {
    if (c==B00100001) c = 0x05; 
    if (c==B00100010) c = 0x06; 
    if (c==B00100100) c = 0x07; 
    if (c==B00101000) c = 0x08;
    delay(100);
    resetPort0();
    return c;
  }


  Wire.beginTransmission(0x20);
  Wire.write(0x02);
  Wire.write(B10110000); // check row L3
  Wire.endTransmission(); 

  Wire.beginTransmission(0x20);  
  Wire.write(0);  // set data pointer
  Wire.endTransmission();
  Wire.requestFrom(0x20, 1);
  c = Wire.read();
  if ((c & 0x4F) > 0x40) {
    if (c==B01000001) c = 0x09; 
    if (c==B01000010) c = 0x10; 
    if (c==B01000100) c = 0x11; 
    if (c==B01001000) c = 0x12;
    delay(100);
    resetPort0();
    return c;
  }


  Wire.beginTransmission(0x20);
  Wire.write(0x02);
  Wire.write(B01110000); // check row L4
  Wire.endTransmission(); 

  Wire.beginTransmission(0x20);  
  Wire.write(0);  // set data pointer
  Wire.endTransmission();
  Wire.requestFrom(0x20, 1);
  c = Wire.read();
  if ((c & 0x8F) > 0x80) {
    if (c==B10000001) c = 0x13; 
    if (c==B10000010) c = 0x14; 
    if (c==B10000100) c = 0x15; 
    if (c==B10001000) c = 0x16;
    delay(100);
    resetPort0();
    return c;
  }



}


void  resetPort0()   {

  Wire.beginTransmission(0x20);  // 
  Wire.write(0x02);  // pointer
  Wire.write(0x00);  // clear bits 4-7 PORT0
  Wire.endTransmission(); 

}