/*
* A program which changes the state of 3 external LEDs
* -	In the low state
* -	Rising edge
*
* SYNTAX: attachInterrupt(interrupt, ISR, mode)
* interrupt: the number of the interrupt. Allowed data types: int.
* ISR: the ISR to call when the interrupt occurs; this function must take no parameters and return nothing. 
*      This function is sometimes referred to as an interrupt service routine.
* mode: defines when the interrupt should be triggered. Four constants are predefined as valid values:
* - LOW to trigger the interrupt whenever the pin is low,
* - CHANGE to trigger the interrupt whenever the pin changes value
* - RISING to trigger when the pin goes from low to high,
* - FALLING for when the pin goes from high to low.
*/

int LedPin1 = 8;
int LedPin2 = 9;
int LedPin3 = 10;

volatile int state = LOW; // state is changed in the ISR , hence declared as volatile.

void setup()
{
 pinMode(LedPin1, OUTPUT); // set to output
 pinMode(LedPin2, OUTPUT); // set to output
 pinMode(LedPin3, OUTPUT); // set to output
 attachInterrupt(1, blink, CHANGE); // turns on interrupt on digital pin 3 with MODE=CHANGE
 //attachInterrupt(1, blink, LOW); // turns on interrupt on digital pin 3 with MODE=LOW
 //attachInterrupt(1, blink, RISING); // turns on interrupt on digital pin 3 with MODE=RISING
 //attachInterrupt(1, blink, FALLING); // turns on interrupt on digital pin 3 with MODE=FALLING
 // ISR named blink 
}

void loop()
{
 digitalWrite(LedPin1, state);
 digitalWrite(LedPin2, state);
 digitalWrite(LedPin3, state);

}
 
void blink() // ISR whenever digital pin 3 changes.
{
 state = !state; 
}