RM0090: Reference manual - STMicroelectronics

Advanced-control timers (TIM1&TIM8) RM0090
14.3.4 Clock selection
The counter clock can be provided by the following clock sources:
● Internal clock (CK_INT)
● External clock mode1: external input pin
● External clock mode2: external trigger input ETR
● Internal trigger inputs (ITRx): using one timer as prescaler for another timer, for
example, you can configure Timer 1 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), 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 92 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 92. Control circuit in normal mode, internal clock divided by 1
Internal clock
CEN=CNT_EN
Counter clock = CK_CNT = CK_PSC
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.
Figure 93. TI2 external clock connection example
TI2
363/1416 Doc ID 018909 Rev 3
UG
CNT_INIT
Counter register 31 32 33 34 35 36 00 01 02 03 04 05 06 07
TIMx_SMCR
TS[2:0]
ITRx
0xx
TI2F
or
TI1F
or
or encoder
mode
Filter
TI2F_Rising
Edge
Detector TI2F_Falling
0
1
TI1_ED
TI1FP1
TI2FP2
ETRF
100
101
110
111
TRGI
ETRF
external clock
mode 1 CK_PSC
external clock
mode 2
ICF[3:0]
TIMx_CCMR1
CC2P
TIMx_CCER
CK_INT internal clock
mode
(internal clock)
ECE SMS[2:0]
TIMx_SMCR