Obsolete

Product(s)

- Obsolete

Product(s)

Obsolete

Product(s)

- Obsolete

Product(s)

Calibration software

AN2326

4/20

Figure 2.

Using the timer input capture to measure the mains frequency

To measure the frequency, the software uses the Lite Timer input capture (LTIC) so that on

each edge of the mains the value of the free running counter is stored as shown in Figure 2..

Then the microcontroller calculates the elapsed time between the two edges of the mains.

This time is given by the following equation:

where nbover represents the number of counter overflows during the measurement, capture

1 and capture 2 are the values captured on the free running counter when an edge occurs

on the mains and F9h is the overflow value of the free running counter.

If the RC oscillator frequency is equal to 1 MHz, the result time will be 138h for European

standard (220V/50Hz) or 104h for US standard mains (110V/60Hz), so these are the

reference values.

This measurement result is compared to the reference value and, depending on the result of

the comparison, the microcontroller adds to or subtracts from the current RCCR/SICSR

register values.

1.2

Basic version

In this version the measurement is done only once for each dichotomization step. This

allows the calibration software to be light and fast. It requires only 128 bytes of program

memory and 5 bytes of RAM during calibration. The calibration takes less than 200 ms to be

completed.

The software works as shown in the following flowchart. The assembly code and a more

detailed flowchart can be found in Section 4.

Free-running

Counter

Mains

Capture 1

Capture 2

Overflow

0h

F9h

time

nbover

F9h

capture2

capture1

–

+

×

=