t13 and tx5 PWM datasheet contradictions

1 post / 0 new
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0


Section 11.7.3 says:

"In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared on the Compare Match between TCNT0 and OCR0x, and set at BOTTOM."


However tables11-3 & 11-6 say OC is set at TOP for COM0 bits = 10


This is the same in the t25/45/85 datasheet.


In my testing, the output is set at the transition from top to bottom.  i.e. running the timer for 1 clock with TCNT0 starting at 255 results in OC set, while running for 1 clock with TCNT0 starting at 254 leaves OC clear.

So both sections are wrong, in non-inverting mode OC is not set at BOTTOM or TOP, it's only set at the transition.


Another thing I figured out when playing with PWM is that in both inverting and non-inverting mode, the OC bit starts as cleared.  That means the first cycle (with TCNT0 starting at 0) in non-inverting mode is low for 100% of the time.



I have no special talents.  I am only passionately curious. - Albert Einstein