I am a new user of Arduino. I used to work with PIC Microcontrollers. This is the first time I am using an Arduino board.
The board I am using is the Arduino Duemilanove. I have written a sample C code using Interrupt Service Routine (ISR). According to what I have learnt about Arduino my code should work correctly. But I have a problem.
I have attached an LED to the PIN13 of the Arduino. Considering the code I have provided below, The LED should flash. But it does not. Can anyone please let me now what I am doing wrong?
Regards
Ehsan
Here is the code:
int ledPin = 13;
void setup()
{
pinMode(ledPin, OUTPUT);
cli(); // Disable interrupts while setting registers
TCCR2A = 0; // Reset control registers
TCCR2B = 0; // Reset control registers
TCCR2A |= (1 << WGM21); // Clear Timer on Compare Match (CTC) Mode
TCCR2B |= (1 << CS20); // Prescaler x1
OCR2A = 100000; // Set compared value
ASSR &= ~(1 << AS2); // Use system clock for Timer/Counter2
TIMSK2 = 0; // Reset Timer/Counter2 Interrupt Mask Register
TIMSK2 |= (1 << OCIE2A); // Enable Output Compare Match A Interrupt
sei(); // Enable interrupts once registers have been update
}
void loop()
{
digitalWrite(ledPin,HIGH);
}
ISR(TIMER2_COMPA_vect) // Interrupt service run when Timer/Counter2 reaches OCR2A
Suggestion number 1:
Make the ISR as simple as possible (but no simpler).
Suggestion number 2:
Don't use loops trying to get predictable, repeatable delays.
//
// Set up Timer2 for an interrupt every 10 usec.
// Toggle the LED and print the value of millis()
// after every 100,000 interrupts. (Every second
// or so.)
//
// The Interrupt Service routine simply increments a
// global variable.
//
// When the variable reaches 100,000, the loop() resets
// the variable, toggles the LED state, and performs a
// printout.
//
int ledPin = 13;
void setup()
{
Serial.begin(9600);
pinMode(ledPin, OUTPUT);
// Disable interrupts while setting registers
cli();
// Reset control registers
TCCR2A = 0;
TCCR2B = 0;
// Clear Timer on Compare Match (CTC) Mode
TCCR2A |= (1 << WGM21);
// Prescaler x1
TCCR2B |= (1 << CS20);
// Interrupt every 160/16e6 = 10 usec
OCR2A = 159;
// Use system clock for Timer/Counter2
ASSR &= ~(1 << AS2);
// Reset Timer/Counter2 Interrupt Mask Register
TIMSK2 = 0;
// Enable Output Compare Match A Interrupt
TIMSK2 |= (1 << OCIE2A);
// Enable interrupts once registers have been updated
sei();
}
unsigned long int_count = 0;
unsigned long max_count = 100000;
int led_state = 0;
void loop()
{
if (int_count >= max_count) {
int_count = 0;
Serial.println(millis());
digitalWrite(ledPin, led_state);
led_state = 1 - led_state;
}
}
// This ISR is run when Timer/Counter2 reaches OCR2A
ISR(TIMER2_COMPA_vect)
{
++int_count;
}
Maybe the problem is hardware not software. I have two Arduino (Decimilia and Mega) they both come with an inbuilt LED connected to Pin 13. Maybe by connecting another LED to pin 13 you created a hardware problem? So try disconnecting your LED and see if the in-built LED flashes
Also the Arduiono development environment includes a simple program example for flashing a LED. You'll find it at File>Examples>Digital>Blink. If this work at least you know you don't have a hardware problem !
