![]() Please note that every timer of an Uno has 2 OCR registers (Mega has 3), for 2 PWM outputs. ![]() In other PWM modes it counts up to MAX, then again down to BOTTOM, and toggles the output pin on every compare match. In fast PWM mode the output pin, related to the selected OCR, is set on count zero (BOTTOM), and cleared on a compare match. This value must not exceed MAX, so that it compares equal once, whenever the timer counts up or down. Then the timer counts continuously from 0 to 99, equivalent to 100 steps or 100µs or 10kHz.įinally you set an OCR (output compare register) to the desired PWM duty cycle. If you want 10kHz, equivalent to 100µs, and get 1µs clock from the 1:16 prescaler, you set e.g. ![]() Next some timers can be configured to count up to a specific MAX value. Not all prescaler factors can be programmed, though, see the control register descriptions for the various timers. If you set the prescaler to 1:16, you'll get 1MHz from a 16MHz clock frequency, or one period every microsecond. It's possible to get any number of odd PWM frequencies, like 10kHz, by configuring a timer accordingly.įirst comes the timer prescaler, that divides the system clock by a power of 2, up to 2^10=1024. Am I thinking too digital? (Mind you: I am a retired Directional Drliler, normally drilling for Oil and Gas, with a ChemEng background.)īut, any way guys, you BOTH helped a lot. The numbers for sure.īut, I do have a question: If I translate the Binary number to Numerical, I see no direct relationship in divider and divider. It initially confused me, but now it is more oe less clear. Terrykings' paper shows that not all dividers, such as divider 4, are applicable this is pin dependant see Terry's table attached. But I now see that 4kHz is acceptable to have my laser firing up in 5 mSec's, with a 0.15V variance. I phrased it wrong in my post I should have said around 10kHz. Re 10 kHz: I do understand that I will not get 10kHz exactly. And indeed, as you showed: it comes to 490 Hz. 256/2 was never mentioned in none of the posts I've checked. You could get possibly 15625 Hz (15.625 kHz), but you cannot get 10000 Hz (10 kHz) exactly as a PWM frequency. PWM frequencies can be much more speedy by factor 2, 4,8 or 16 I think, if you manipulate some divider registers in a different way.īut it is NOT POSSIBLE to get every PWM frequency you might want. Higher PWM output frequencies would require mangling with internal timer registers of the Atmega328 in your sketch. Whether the default PWM frequency on an UNOs PWM output is actually 490.196Hz or 976.5625Hz simply depends on the PWM pin number used by default. ![]() The Atmega328 is a 8-bit microcontroller. The dividers 255 (phase-correct PWM) or 256 (fast PWM) are caused by the fact, that it is 8-bit PWM which we are talking about. The default PWM frequency calculation for"fast PWM" with an UNO is: The default PWM frequency calculation for phase-correct PWM with an UNO is: I also found that the default divider is 64 and that PWM- frequency is Clock-speed divided by the divider.īut, for an Arduino Uno (16 MHz) I than calculate 250 kHz ( = 16 MHz / 64).Īrduino UNO PWM pins operate in one out of two PWM modes (epending on the internal hardware timer used):Įither "fast PWM mode" or "phase-correct PWM mode" With googling around, I found that the default PWM frequency of an Arduino Uno PWM pin D11 is around 500 Hz.
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