DocID022500 Rev 4

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AN4013

General-purpose timer modes

36

Particular case

To facilitate the input capture measurement, the timer counter is reset after each rising edge

detected on the timer input channel by:



selecting TIxFPx as the input trigger by setting the TS bits in the SMCR register



selecting the reset mode as the slave mode by configuring the SMS bits in the SMCR

register

Using this configuration, when an edge is detected, the counter is reset and the period of the

external signal is automatically given by the value on the CCRx register. This method is

used only with channel 1 or channel 2.

In this case, the input capture prescaler (ICPSC) is not considered in the period

computation.

The period is computed as follows:

Period = CCRx /(TIMx_CLK *(PSC+1)* polarity_index(1))

The polarity index is 1 if rising or falling edge is used, and 2 if both edges are used.

For more details on using the timer in this mode, refer to the examples provided in the

STM32xx standard peripheral libraries in the /Project/STM32xx_StdPeriph_Examples/

TIM/InputCapture folder.

STM32Cube F3 firmware package includes examples in the following directories:



Projects\STM32F3-Discovery\Examples\TIM\TIM_InputCapture,



Projects\STM32373C_EVAL\Examples\TIMTIM_InputCapture,



Projects\STM32303E_EVAL\Examples\TIM\TIM_InputCapture and



Projects\STM32303C_EVAL\Examples\TIM\TIM_InputCapture

2.4

Timer output compare mode

To control an output waveform, or to indicate when a period of time has elapsed, the timer is

used in one of the following output compare modes. The main difference between these

modes is the output signal waveform.



Output compare timing: The comparison between the output compare register CCRx

and the counter CNT has no effect on the outputs. This mode is used to generate a

timing base.



Output compare active: Set the channel output to active level on match. The OCxRef

signal is forced high when the counter (CNT) matches the capture/compare register

(CCRx).



Output compare inactive: Set channel to inactive level on match. The OCxRef signal

is forced low when the counter (CNT) matches the capture/compare register (CCRx).



Output compare toggle: OCxRef toggles when the counter (CNT) matches the

capture/compare register (CCRx).



Output compare forced active/inactive: OCREF is forced high (active mode) or low

(inactive mode) independently from counter value.