Peripheral firmware examples description

AN4157

20/24

Doc ID 023629 Rev 1

3.23

TIM PWM input example

3.23.1

Purpose

This example shows how to use the TIM peripheral to measure the frequency and duty cycle

of an external signal.

3.23.2

Description

TIMxclock (TIMxCLK) is SystemCoreClock, and TIMx prescalers are set to 0 so that TIMx

counter clock is SystemCoreClock (72 MHz).

TIM2 is configured in PWM Input mode: the external signal is connected to TIM2 Channel2

used as an input pin.

To measure the frequency and the duty cycle, TIM2_CCR2 interrupt request is used, so that

the frequency and the duty cycle of the external signal are computed in the

TIM2_IRQHandler routine.

The “Frequency” variable contains the external signal frequency:

●

TIM2 counter clock = SystemCoreClock,

●

Frequency = TIM2 counter clock / TIM2_CCR2 in Hz,

The “DutyCycle” variable contains the external signal duty cycle:

DutyCycle = (TIM2_CCR1*100)/(TIM2_CCR2) in %.

The minimum frequency value to measure is 915 Hz (TIM2 counter clock / CCR MAX).

Note:

Connect the external signal to measure the TIM2 CH2 pin (PA01).

3.24

TIM rettrigreable one pulse mode example

3.24.1

Purpose

This example shows how to use the TIM peripheral to generate a Retrigerrable One pulse

Mode after a Rising edge of an external signal is received in Timer Input pin.

3.24.2

Description

In this example, we want to obtain aTIM2 counter clock of 36 MHz and a TIM2 inputs clock

(TIM2CLK) equal to systemCoreClock (72 MHz):

Prescaler = (TIM2CLK / TIM2 counter clock) - 1

The Autoreload value is 65535 (TIM2->ARR). Aa a result the maximum frequency to trigger

the TIM2 input is:

36000000/65535 = 549.3 Hz.