Low-speed internal oscillator measurement

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Low-speed internal oscillator measurement

The internal LSI RC oscillator is a low-power clock source. In the STM32F0x microcontroller

family, an internal and indirect connection is provided between the internal RC oscillator LSI

and the embedded timer TIM14 to facilitate the measurement procedure.

4.1

Measurement principle

The internal RC oscillator measurement procedure consists in running the timer counter

using the HSI clock, configuring the internal RC oscillator LSI as the clock source for RTC,

configuring the timer in Input capture mode and then connecting the RTC to the timer.

Figure 14 shows the configuration used to perform an LSI measurement.

Figure 14. LSI measurement configuration

After enabling the timer counter, when the first rising edge of the internal oscillator signal to

be measured occurs, the timer counter value is captured and then stored in

IC1ReadValue1. On the second rising edge, the timer counter is captured again and stored

in IC1ReadValue2. The elapsed time between two consecutive rising edges of the clock

represents an entire period. Figure 15 shows the timing diagram of an internal RC oscillator

measurement.

Note:

MCO can be also used for this purpose.