DocID018909 Rev 11
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RM0090
General-purpose timers (TIM9 to TIM14)
687
Figure 190. Control circuit in normal mode, internal clock divided by 1
External clock source mode 1(
TIM9 and TIM1
2
)
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.
Figure 191. TI2 external clock connection example
For example, to configure the upcounter to count in response to a rising edge on the TI2
input, use the following procedure:
1.
Configure channel 2 to detect rising edges on the TI2 input by writing CC2S = ‘01’ in
the TIMx_CCMR1 register.
2. Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1
register (if no filter is needed, keep IC2F=’0000’).
3. Select the rising edge polarity by writing CC2P=’0’ and CC2NP=’0’ in the TIMx_CCER
register.
4. Configure the timer in external clock mode 1 by writing SMS=’111’ in the TIMx_SMCR
register.
5. Select TI2 as the trigger input source by writing TS=’110’ in the TIMx_SMCR register.
6. Enable the counter by writing CEN=’1’ in the TIMx_CR1 register.
Note:
The capture prescaler is not used for triggering, so you don’t need to configure it.
When a rising edge occurs on TI2, the counter counts once and the TIF 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 TI2 input.
Internal clock
00
Counter clock = CK_CNT = CK_PSC
Counter register
01 02 03 04 05 06 07
32 33 34 35 36
31
CEN=CNT_EN
UG
CNT_INIT
CK_INT
external clock
mode 1
internal clock
mode
TRGI
TI1F
TI2F or
or
or
(internal clock)
CK_PSC
TIMx_SMCR
SMS[2:0]
ITRx
TI1_ED
TI1FP1
TI2FP2
TIMx_SMCR
TS[2:0]
TI2
0
1
TIMx_CCER
CC2P
Filter
ICF[3:0]
TIMx_CCMR1
Edge
Detector
TI2F_Rising
TI2F_Falling
110
0xx
100
101