Arduino Code for Keyfob Decoder - Using Interrupts and Low Level AVR Bit Shifts

Low Level AVR Keyfob

//ECET2700 Paralax Keyfob Decoder - Interrupt Driven
//Meant for Arduino Xplained Mini but portable to any Arduino or derivative
//Andrei Aldea 2/25/2019

#define buttonReadDelay 200 //200 milliseconds we give the fob between when we want to read and when VT interrupt goes high

void setup()
{
  DDRC  = 0x00; //SET Register C to INPUTS
  DDRD  = 0xFF; //Outputs, Bottom Two bits are Serial, 3rd bit is Interrupt
  DDRB  = 0xFF; //OutputsOnly need bottom three bits
  PORTD = 0x00; //Initialize to Off
  PORTB = 0x00; //Initalize to Off

  Serial.begin(115200); //Gotta go fast
  attachInterrupt(digitalPinToInterrupt(2), key_decoder, RISING); //Trigger interrupt on Rising Edge
  while (!Serial.available() ) {
    //Wait for Serial to become available... if it's not for some reason... good for native USB boards like 32u4
  } 
  Serial.println("Decoder Started");
}

void loop()
{
  //Do nothing here, because interrupts!
}

void key_decoder()
{
  delay(buttonReadDelay);
  Serial.print("Interrupt Tirggered: ");
  Serial.print(PINC, BIN); //Print it in Binary
  Serial.print(" AKA ");
  switch (PINC)
  {
    //OR check individual bits with:  bit = (number >> n) & 1U;
    case 0b00100000: //A
      PORTD ^= 1UL << 4; //Toggle Bit 3
      Serial.println("A");
      break;
    case 0b000010000: //B
      PORTD ^= 1UL << 5; //Toggle Bit 4
      Serial.println("B");
      break;
    case 0b00001000: //C
      PORTD ^= 1UL << 6; //Toggle Bit 5
      Serial.println("C");
      break;
    case 0b00000100: //D
      PORTD ^= 1UL << 7; //Toggle Bit 6
      Serial.println("D");
      break;
    case 0b00110000: //AB
      PORTB ^= 1UL << 2; //Toggle Bit 7
      Serial.println("AB");
      break;
    case 0b00001100: //CD
      PORTB ^= 1UL << 3; //Toggle PortB Bit 0
      Serial.println("CD");
      break;
    case 0b00101000: //AC
      PORTB ^= 1UL << 4; //Toggle PortB Bit 1
      Serial.println("AC");
      break;
    case 0b00010100: //BD
      PORTB  ^= 1UL << 5 ; //Toggle PortB Bit 2
      Serial.println("BD");
      break;
    default:
      Serial.println("Other combo");
      break;
  }
}