Figure 109. Edge-Aligned Pwm Waveforms (Arr=8) - ST STM32F412 Reference Manual

Advanced-control timers (TIM1&TIM8)
PWM edge-aligned mode
•
Upcounting configuration
Upcounting is active when the DIR bit in the TIMx_CR1 register is low. Refer to
Upcounting
In the following example, we consider PWM mode 1. The reference PWM signal
OCxREF is high as long as TIMx_CNT < TIMx_CCRx else it becomes low. If the
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 109
TIMx_ARR=8.
Counter register
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
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
TIMx_CR1 register is updated by hardware and must not be changed by software. Refer to
Center-aligned mode (up/down
438/1163
mode.
shows some edge-aligned PWM waveforms in an example where

Figure 109. Edge-aligned PWM waveforms (ARR=8)

0 1
OCXREF
CCxIF
OCXREF
CCxIF
'1'
OCXREF
CCxIF
'0'
OCXREF
CCxIF
mode.
counting).
RM0402 Rev 6
2 3 4 5 6
RM0402
7 8 0 1
MS31093V1