EM357-RTR datasheet(130/240 Pages) ETC2

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EM351 / EM357

Figure 9-13. TI2 External Clock Connection Example

For example, to configure the up-counter to count in response to a rising edge on the TI2 input, use the

following procedure:

Configure channel 2 to detect rising edges on the TI2 input: Write TIM_CC2S = 01 in the TIMx_CCMR1

Configure the input filter duration: Write the TIM_IC2F bits in the TIMx_CCMR1 register (if no filter is

needed, keep TIM_IC2F = 0000).

Note: The capture prescaler is not used for triggering, so it does not need to be configured.

Select rising edge polarity: Write TIM_CC2P = 0 in the TIMx_CCER register.

Configure the timer in external clock mode 1: Write TIM_SMS = 111 in the TIMx_SMCR register.

Select TI2 as the input source: Write TIM_TS = 110 in the TIMx_SMCR register.

Enable the counter: Write TIM_CEN = 1 in the TIMx_CR1 register.

When a rising edge occurs on TI2, the counter counts once and the INT_TIMTIF flag is set. The delay between

the rising edge on TI2 and the actual clock of the counter is due to the resynchronization circuit on the TI2

input. The relationship between rising edges on TI2 and the resulting counter clocks is shown in Figure 9-14.

Figure 9-14. Control Circuit in External Clock Mode 1

9.3.3.3

External Clock Source Mode 2

This mode is selected by writing TIM_ECE = 1 in the TIMx_SMCR register. The counter can count at each rising

or falling edge on the external trigger input ETR.

The TIM_EXTRIGSEL bits in the TIMx_OR register select a clock signal that drives ETR, as shown in Table 9-2.

9-10

120-035X-000D

Preliminary

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