General-purpose timers (TIM9 and TIM11) RM0401
398/771 RM0401 Rev 3
16.3.3 Clock selection
The counter clock can be provided by the following clock sources:
• Internal clock (CK_INT)
• External clock mode1 (for TIM9): external input pin (TIx)
• Internal trigger inputs (ITRx) (for TIM9): connecting the trigger output from another
timer.
Internal clock source (CK_INT)
The internal clock source is the default clock source for TIM11.
For TIM9, the internal clock source is selected when the slave mode controller is disabled
(SMS=’000’). The CEN bit in the TIMx_CR1 register and the UG bit in the TIMx_EGR
register are then used as control bits and can be changed only by software (except for UG
which remains cleared). As soon as the CEN bit is programmed to 1, the prescaler is
clocked by the internal clock CK_INT.
Figure 143 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 143. Control circuit in normal mode, internal clock divided by 1
External clock source mode 1(TIM9)
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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