STM8S datasheet(174/467 Pages) STMICROELECTRONICS

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16-bit advanced control timer (TIM1)

RM0016

174/467

DocID14587 Rev 14

17.5.7

PWM mode

Pulse width modulation mode allows you to generate a signal with a frequency determined

by the value of the TIM1_ARR register and a duty cycle determined by the value of the

TIM1_CCRi registers.

The PWM mode can be selected independently on each channel (one PWM per OCi output)

by writing 110 (PWM mode 1) or 111 (PWM mode 2) in the OCiM bits in the TIM1_CCMRi

registers. The corresponding preload register must be enabled by setting the OCiPE bits in

the TIM1_CCMRi registers. The auto-reload preload register (in up-counting or center-

aligned modes) may be optionally enabled by setting the ARPE bit in the TIM1_CR1

As the preload registers are transferred to the shadow registers only when an UEV occurs,

all registers have to be initialized by setting the UG bit in the TIM1_EGR register before

starting the counter.

OCi polarity is software programmable using the CCiP bits in the TIM1_CCERi registers. It

can be programmed as active high or active low. The OCi output is enabled by a

combination of CCiE, MOE, OISi, OSSR and OSSI bits (TIM1_CCERi and TIM1_BKR

registers). Refer to the TIM1_CCERi register descriptions for more details.

In PWM mode (1 or 2), TIM1_CNT and TIM1_CCRi are always compared to determine

whether TIM1_CCRi

≤ TIM1_CNT or TIM1_CNT≤ TIM1_CCRi (depending on the direction

of the counter).

The timer is able to generate PWM in edge-aligned mode or center-aligned mode

depending on the CMS bits in the TIM1_CR1 register.

PWM edge-aligned mode

Up-counting configuration

Up-counting is active when the DIR bit in the TIM1_CR1 register is low.

Example

This example uses PWM mode 1. The reference PWM signal, OCiREF, is high as long as

TIM1_CNT < TIM1_CCRi. Otherwise, it becomes low. If the compare value in TIM1_CCRi is

greater than the auto-reload value (in TIM1_ARR) then OCiREF is held at 1. If the compare

value is 0, OCiREF is held at 0. Figure 70 shows some edge-aligned PWM waveforms in an

example where TIM1_ARR = 8.

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