Advanced-control timers (TIM1&TIM8) RM0090
516/1731 DocID018909 Rev 11
Figure 87. Counter timing diagram with prescaler division change from 1 to 2
Figure 88. Counter timing diagram with prescaler division change from 1 to 4
17.3.2 Counter modes
Upcounting mode
In upcounting mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register), then restarts from 0 and generates a counter overflow event.
If the repetition counter is used, the update event (UEV) is generated after upcounting is
repeated for the number of times programmed in the repetition counter register plus one
(TIMx_RCR+1). Else the update event is generated at each counter overflow.
Setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event.
The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
CK_PSC
00
CEN
Timer clock = CK_CNT
Counter register
Update event (UEV)
0
F9 FA FB FCF7
Prescaler control register
01
Write a new value in TIMx_PSC
01 02 03
Prescaler buffer
01
Prescaler counter
0
1 0 1 0 1 0 1
F8
CK_PSC
00
CEN
Timer clock = CK_CNT
Counter register
Update event (UEV)
0
F9 FA FB FCF7
Prescaler control register
03
Write a new value in TIMx_PSC
Prescaler buffer
03
Prescaler counter
0
1 2 3 0 1 2 3
F8 01
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