DocID16612 Rev 6

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AN3101

High speed internal oscillator calibration

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2.2

Hardware implementation

2.2.1

Case where LSE is used as the reference frequency

STM8L05xxx/15xxx, STM8L162xx and STM8AL31xx/3Lxx microcontroller devices offer a

very useful feature, i.e. the ability to connect low speed oscillators (LSI or LSE) to Timer 2

channel 1. Thus, the LSE clock can be used as the reference signal for HSI calibration and

no additional hardware connections are required. Only the LSE oscillator should be

connected to OSC32_IN and OSC32_OUT.

Figure 4 shows the hardware connections needed for HSI calibration using LSE as an

accurate frequency source for calibration.

Figure 4. Hardware connection using LSE as the reference frequency

2.2.2

Case where another source is used as the reference frequency

Any signal with accurate frequency can be used for HSI calibration and the mains frequency

is one of the possibilities.

Note:

Refer to the AN2868 application note (“STM32F10xx internal RC oscillator (HSI)

calibration”) for more details about using mains frequency for calibration.

As indicated in Figure 5, the reference frequency must be connected to Timer 2 channel 1

(PB0 pin).

Figure 5. Hardware connection using external reference frequency