Pwm Mode; Figure 117. Output Compare Mode, Toggle On Oc1 - ST STM32F100 Series Reference Manual

RM0041
The TIMx_CCRx register can be updated at any time by software to control the output
waveform, provided that the preload register is not enabled (OCxPE=0, else TIMx_CCRx
shadow register is updated only at the next update event UEV). An example is given in
Figure 117.
TIMx_CNT
TIMx_CCR1
OC1REF = OC1
13.3.9

PWM mode

Pulse width modulation mode allows generating a signal with a frequency determined by the
value of the TIMx_ARR register and a duty cycle determined by the value of the
TIMx_CCRx register.
The PWM mode can be selected independently on each channel (one PWM per OCx
output) by writing 110 (PWM mode 1) or '111 (PWM mode 2) in the OCxM bits in the
TIMx_CCMRx register. The user must enable the corresponding preload register by setting
the OCxPE bit in the TIMx_CCMRx register, and eventually the auto-reload preload register
by setting the ARPE bit in the TIMx_CR1 register.
As the preload registers are transferred to the shadow registers only when an update event
occurs, before starting the counter, the user has to initialize all the registers by setting the
UG bit in the TIMx_EGR register.
OCx polarity is software programmable using the CCxP bit in the TIMx_CCER register. It
can be programmed as active high or active low. OCx output is enabled by the CCxE bit in
the TIMx_CCER register. Refer to the TIMx_CCERx register description for more details.
In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine
whether TIMx_CCRx≤TIMx_CNT or TIMx_CNT≤TIMx_CCRx (depending on the direction of
the counter). However, to comply with the ETRF (OCREF can be cleared by an external
event through the ETR signal until the next PWM period), the OCREF signal is asserted
only:
•
When the result of the comparison changes, or
•
When the output compare mode (OCxM bits in TIMx_CCMRx register) switches from
the "frozen" configuration (no comparison, OCxM='000) to one of the PWM modes
(OCxM='110 or '111).
This forces the PWM by software while the timer is running.

Figure 117. Output compare mode, toggle on OC1

Write B201h in the CC1R register
0039 003A
003A
RM0041 Rev 6
General-purpose timers (TIM2 to TIM5)
003B
Match detected on CCR1
Interrupt generated if enabled
B200 B201
B201
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