Figure 72. Edge-Aligned Pwm Waveforms (Arr=8) - ST STM32F100 Series Reference Manual

Advanced-control timer (TIM1)
compare value in TIMx_CCRx is greater than the auto-reload value (in TIMx_ARR)
then OCxREF is held at '1'. If the compare value is 0 then OCxRef is held at '0'.
Figure 72
TIMx_ARR=8.
CCRx=4
CCRx=8
CCRx>8
CCRx=0
•
Downcounting configuration
Downcounting is active when DIR bit in TIMx_CR1 register is high. Refer to
Downcounting mode
In PWM mode 1, the reference signal OCxRef is low as long as
TIMx_CNT > TIMx_CCRx else it becomes high. If the compare value in TIMx_CCRx is
greater than the auto-reload value in TIMx_ARR, then OCxREF is held at '1'. 0% PWM
is not possible in this mode.
PWM center-aligned mode
Center-aligned mode is active when the CMS bits in TIMx_CR1 register are different from
'00' (all the remaining configurations having the same effect on the OCxRef/OCx signals).
The compare flag is set when the counter counts up, when it counts down or both when it
counts up and down depending on the CMS bits configuration. The direction bit (DIR) in the
238/709
shows some edge-aligned PWM waveforms in an example where

Figure 72. Edge-aligned PWM waveforms (ARR=8)

0
Counter register
OCXREF
CCxIF
OCXREF
CCxIF
OCXREF '1'
CCxIF
'0'
OCXREF
CCxIF
1 2 3 4 5
RM0041 Rev 6
6 7 8 0 1
RM0041
MS31093V1