STM32W108HB datasheet(174/278 Pages) STMICROELECTRONICS

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General-purpose timers

STM32W108HB STM32W108CC STM32W108CB STM32W108CZ

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Doc ID 16252 Rev 14

This allows software to force a PWM output to a particular state while the timer is running.

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

depending on the CMS bits in the TIMx_CR1 register.

PWM edge-aligned mode: up-counting configuration

Up-counting is active when the DIR bit in the TIMx_CR1 register is low. Refer to Up-counting

mode on page 159.

The following example uses PWM mode 1. The reference PWM signal OCyREF is high as

long as TIMx_CNT < TIMx_CCRy, otherwise it becomes low. If the compare value in

TIMx_CCRy is greater than the auto-reload value in TIMx_ARR, then OCyREF is held at 1.

If the compare value is 0, then OCyREF is held at 0. Figure 36 shows some edge-aligned

PWM waveforms in an example, where TIMx_ARR = 8.

Figure 36.

Edge-aligned PWM waveforms (ARR = 8)

PWM edge-aligned mode: down-counting configuration

Down-counting is active when the DIR bit in the TIMx_CR1 register is high. Refer to Down-

counting mode on page 161 for more information.

In PWM mode 1, the reference signal OCyREF is low as long as TIMx_CNT > TIMx_CCRy,

otherwise it becomes high. If the compare value in TIMx_CCRy is greater than the auto-

reload value in TIMx_ARR, then OCyREF is held at 1. Zero-percent PWM is not possible in

this mode.

PWM center-aligned mode

Center-aligned mode is active except when the CMS bits in the TIMx_CR1 register are 00

(all configurations where CMS is non-zero have the same effect on the OCyREF/OCy

signals). The compare flag is set when the counter counts up, when it counts down, or 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 counting) on page 162 for more information.

Counter register

‘1

‘0

OCxREF

CCyIE

OCxREF

CCyIE

OCxREF

TIMx_CCRy=4

TIMx_CCRy=8

CCyIE

TIMx_CCRy>8

TIMx_CCRy=0

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