RM0390 Rev 4 533/1328
RM0390 General-purpose timers (TIM2 to TIM5)
581
17.3.3 Clock selection
The counter clock can be provided by the following clock sources:
• Internal clock (CK_INT)
• External clock mode1: external input pin (TIx)
• External clock mode2: external trigger input (ETR) available on TIM2, TIM3 and TIM4
only.
• Internal trigger inputs (ITRx): using one timer as prescaler for another timer, for
example, you can configure Timer to act as a prescaler for Timer 2. Refer to Using one
timer as prescaler for another for more details.
Internal clock source (CK_INT)
If the slave mode controller is disabled (SMS=000 in the TIMx_SMCR register), then the
CEN, DIR (in the TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual
control bits and can be changed only by software (except UG which remains cleared
automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal
clock CK_INT.
Figure 178 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 178. Control circuit in normal mode, internal clock divided by 1
External clock source mode 1
This mode is selected when SMS=111 in the TIMx_SMCR register. The counter can count at
each rising or falling edge on a selected input.
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