I want to be able to use the Arduino Due PWM at higher resolution and frequency than what is available by default. I use IDE 1.6.8, that was the most recent a few weeks ago when I installed it (I think 1.6.9 may be on its way now). After searching on the internet and experimenting with the board and an oscilloscope, I got to the following conclusions:
#define PWM_FREQUENCY 20000 // changed from 1000
#define TC_FREQUENCY 20000 // changed from 1000
#define PWM_MAX_DUTY_CYCLE 4095 // changed from 255
#define PWM_MIN_DUTY_CYCLE 0
#define PWM_RESOLUTION 12 // changed from 8
I post this content here as it took me a while to figure out everything and to check on the oscilloscope etc, and I could not find those answers on stackoverflow. I also have two questions:
Is it OK (as it looks like from the tests I did) to modify the PWM and TC frequencies? May it interact with other core functions / libraries?
Is there a reason for the default values of PWM max duty cycle and resolution, other than backward compatibility?
You can do this with the PWM frequency divisors: http://forum.arduino.cc/index.php?topic=16612#msg121031
This is implemented in the PWMfrequency library: http://playground.arduino.cc/Code/PwmFrequency which basically looks like this:
void setPwmFrequency(int pin, int divisor) {
byte mode;
if(pin == 5 || pin == 6 || pin == 9 || pin == 10) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 64: mode = 0x03; break;
case 256: mode = 0x04; break;
case 1024: mode = 0x05; break;
default: return;
}
if(pin == 5 || pin == 6) {
TCCR0B = TCCR0B & 0b11111000 | mode;
} else {
TCCR1B = TCCR1B & 0b11111000 | mode;
}
} else if(pin == 3 || pin == 11) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 32: mode = 0x03; break;
case 64: mode = 0x04; break;
case 128: mode = 0x05; break;
case 256: mode = 0x06; break;
case 1024: mode = 0x07; break;
default: return;
}
TCCR2B = TCCR2B & 0b11111000 | mode;
}
}