Advanced-control timers (TIM1&TIM8)
RM0090
526/1731
DocID018909 Rev 11
17.3.4 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
one timer as prescaler for another timer
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.
shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 107. 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.
Figure 108. TI2 external clock connection example
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
encoder
mode
external clock
mode 1
external clock
mode 2
internal clock
mode
ETRF
TRGI
TI1F
TI2F or
or
or
(internal clock)
CK_PSC
ECE
TIMx_SMCR
SMS[2:0]
ITRx
TI1_ED
TI1FP1
TI2FP2
ETRF
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
111