SparkFun Forums

[fsphil]

Evening all!

I've noticed an odd thing my AVR Tiny2313. I'm using all four PWM channels to drive some LEDs - real simple stuff - but for some reason I can't get a duty cycle of 0x00 for the channels driven by Timer0. The LEDs are still lit (less than duty at 0x01, but not off). The other two PWMs (which I have configured as 8-bit) don't show this problem.

I can turn the PWM off manually when the duty == 0x00, but I'd like to know why I have to.

Any ideas?

[mkissin]

IIRC, there is a PWM mode on the AVRs that ends up with you having to choose between being able to achieve a PWM of 100% or 0%, but it can't do both. Something along the lines of the compare unit being "less than" or "less than or equal to".

I might be thinking of another chip though.

[fsphil]

No, I think your right. Found this in the data sh**t: (this word is censored?)

The extreme values for the OCR0A Register represents special cases when generating a PWM waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.

Although it says the same for Timer1's fast PWM mode, an effect I'm not seeing.

[fsphil]

Although it says the same for Timer1's fast PWM mode, an effect I'm not seeing.

... which was because I had it configured for Phase Correct mode, not Fast PWM.

Solved!

[fsphil]

Ok, I take that back. Even configured to use fast PWM Timer1 turns off completely when the duty == 0x00.
Anyway - I understand the problem with Timer0 and how to deal with it now and that was the main problem.