Register Update - ST STM32F413 Reference Manual

RM0430
21.4.10

Register update

The LPTIM_ARR register and LPTIM_CMP register are updated immediately after the APB
bus write operation, or at the end of the current period if the timer is already started.
The PRELOAD bit controls how the LPTIM_ARR and the LPTIM_CMP registers are
updated:
• When the PRELOAD bit is reset to '0', the LPTIM_ARR and the LPTIM_CMP registers
are immediately updated after any write access.
•
When the PRELOAD bit is set to '1', the LPTIM_ARR and the LPTIM_CMP registers
are updated at the end of the current period, if the timer has been already started.
The APB bus and the LPTIM use different clocks, so there is some latency between the
APB write and the moment when these values are available to the counter comparator.
Within this latency period, any additional write into these registers must be avoided.
The ARROK flag and the CMPOK flag in the LPTIM_ISR register indicate when the write
operation is completed to respectively the LPTIM_ARR register and the LPTIM_CMP
register.
After a write to the LPTIM_ARR register or the LPTIM_CMP register, a new write operation
to the same register can only be performed when the previous write operation is completed.
Any successive write before respectively the ARROK flag or the CMPOK flag be set, will
lead to unpredictable results.
Figure 219. Waveform generation
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Low-power timer (LPTIM)
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