Figure 152. Update Rate Examples Depending On Mode And Timx_Rcr Register Settings - STMicroelectronics RM0365 Reference Manual

RM0365 Advanced-control timers (TIM1)
In Center aligned mode, for odd values of RCR, the update event occurs either on the
overflow or on the underflow depending on when the RCR register was written and when
the counter was launched: if the RCR was written before launching the counter, the UEV
occurs on the overflow. If the RCR was written after launching the counter, the UEV occurs
on the underflow.
For example, for RCR = 3, the UEV is generated each 4th overflow or underflow event
depending on when the RCR was written.

Figure 152. Update rate examples depending on mode and TIMx_RCR register settings

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