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CALIBRATING THE RC OSCILLATOR OF THE ST7FLITE0 MCU USING THE MAINS

1.3 AVERAGE VERSION

This version uses the method described in Section 1.1 except it performs four measurements

and uses their average for each dichotomization step. It is useful when the mains is noisy. For

instance, when a motor starts it generates a tension pick and this can be considered as a

mains edge.

This version is safer than the basic one but it requires more resources. It uses 136 bytes of

program memory and 11 bytes of RAM during calibration. The calibration takes less than 560

ms to be completed.

The average version works as shown in the following flowchart. The assembly code can be

found in Section 4.

Figure 4. Average software flowchart

Dichotomization

finished?

Initialization of Lite Timer

Average

Increase RCCR

Decrease RCCR

Clock is set to 1 MHz

smaller

greater or equal

Compare

result with

reference

no

yes

calculation

4 measurements and