Internal RC oscillator calibration

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DocID022913 Rev 2

value is 16. An increase/decrease in this trimming value causes an increase/decrease in the

HSI14 frequency. The HSI14 oscillator is fine-tuned in steps of 1% (around 50 kHz).



Writing a trimming value, in the range of 17 to 31, increases the HSI14 frequency.



Writing a trimming value, in the range of 0 to 15, decreases the HSI14 frequency.



Writing a trimming value, equal to 16, causes the HSI14 frequency to keep its default

value.

Figure 3 shows the HSI14 oscillator behavior versus the calibration value. The HSI14

oscillator frequency increases with the calibration value (calibration value = default

HSI14CAL[7:0] + HSI14TRIM[4:0]), except at modulo 16. At these calibration values, the

negative steps can reach three times the positive steps.

Figure 3. HSI14 oscillator trimming characteristics

For the HSI48 oscillator, the calibration value is loaded in HSI48CAL[7:0] bits after reset. Six

trimming bits TRIM [5:0] (in CRS control register) are used for fine-tuning. The default

trimming value is 32. An increase/decrease in this trimming value causes an

increase/decrease in HSI48 frequency.

The HSI48 oscillator is fine-tuned in steps of 1% (around 67 kHz).



Writing a trimming value, in the range of 33 to 63, increases the HSI48 frequency.



Writing a trimming value, in the range of 0 to 31, decreases the HSI48 frequency.



Writing a trimming value, equal to 32, causes the HSI48 frequency to keep its default

value.

Figure 4 shows the HSI48 oscillator behavior versus the calibration value. The HSI48

oscillator frequency increases with the calibration value (calibration value = default

HSI48CAL[7:0] + TRIM[5:0]