DocID018909 Rev 11 615/1731
RM0090 General-purpose timers (TIM2 to TIM5)
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Figure 176. Gating timer 2 with Enable of timer 1
Using one timer to start another timer
In this example, we set the enable of Timer 2 with the update event of Timer 1. Refer to
Figure 174 for connections. Timer 2 starts counting from its current value (which can be
nonzero) on the divided internal clock as soon as the update event is generated by Timer 1.
When Timer 2 receives the trigger signal its CEN bit is automatically set and the counter
counts until we write ‘0 to the CEN bit in the TIM2_CR1 register. Both counter clock
frequencies are divided by 3 by the prescaler compared to CK_INT (f
CK_CNT
= f
CK_INT
/3).
• Configure Timer 1 master mode to send its Update Event (UEV) as trigger output
(MMS=010 in the TIM1_CR2 register).
• Configure the Timer 1 period (TIM1_ARR registers).
• Configure Timer 2 to get the input trigger from Timer 1 (TS=000 in the TIM2_SMCR
register).
• Configure Timer 2 in trigger mode (SMS=110 in TIM2_SMCR register).
• Start Timer 1 by writing ‘1 in the CEN bit (TIM1_CR1 register).
Figure 177. Triggering timer 2 with update of timer 1
TIMER 2-TIF
Write TIF=0
75 00 01
CK_INT
TIMER1-CEN=CNT_EN
TIMER1-CNT
TIMER2-CNT
02
TIMER1-CNT_INIT
AB 00 E7 E8 E9
TIMER2-CNT_INIT
TIMER2
write CNT
TIMER 2-TIF
Write TIF=0
FD
FE FF
00
01
45 47 48
CK_INT
TIMER1-UEV
TIMER1-CNT
TIMER2-CNT
02
46
TIMER2-CEN=CNT_EN
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