Figure 16. Frequency Measurement With Tim11 In Input Capture Mode - ST STM32F423 Reference Manual

Reset and clock control (RCC) for STM32F413/423
Internal/external clock measurement using TIM11 channel1
TIM11 has an input multiplexer which allows choosing whether the input capture is triggered
by the I/O or by an internal clock. This selection is performed through TI1_RMP [1:0] bits in
the TIM11_OR register. The HSE_RTC clock (HSE divided by a programmable prescaler) is
connected to channel 1 input capture to have a rough indication of the external crystal
frequency. This requires that the HSI is the system clock source. This can be useful for
instance to ensure compliance with the IEC 60730/IEC 61335 standards which require to be
able to determine harmonic or subharmonic frequencies (–50/+100% deviations).
128/1324

Figure 16. Frequency measurement with TIM11 in Input capture mode

RM0430 Rev 8
RM0430