//3 Bit Binary Down Counter, counts 7-0 and resets

int counter;   //sets up counter variable
int code;      //sets up code variable

void setup()
{
  DDRD = DDRD | B11111100;   //sets pins 2-7 as outputs, cannot use pins 0 and 1
  Serial.begin(9600);        //starts Serial Monitor
}

void loop()   //a counter 7 to 0
{
  for(counter=7; counter<8; counter--)  //counts down 7-0
  {
    if (counter>=0)   //counts down if counter is more than 0
    {
    PORTD = PORTD & B00000011;   //sets bits 2-7 to zero, leave 0 and 1
    code = (counter<<2);   //shifts variable to pins 2-7, to avoid pins 0 and 1
    PORTD = PORTD | code;   //or's port info with code variable
    Serial.println(PORTD, BIN);  //displays count in binary
    Serial.println(counter);   //displays count in decimal
    delay(500);                //sets half a second between steps
    }
    else
    {
      PORTD = PORTD & B00011111;   //resets the counter once 0 is reached
    }

}
}