A 720mV RMS sine wave, biased to +1.25V is connected to the PB2 pin. PB2 is the COMP1 positive input. The COMP1 negative input is connected to the internal reference voltage (+1.22V) The output of the comparator is connected to PA0 which is the input capture channel 1 input of TIM2 (32-bit) timer. The TIM2 runs from 275MHz clock and it is started in input capture channel1 with interrupt mode. It works, but it measures 119.3Hz instead of 120Hz.
I had to set the comparator mode to COMP_POWERMODE_MEDIUMSPEED because with the COMP_POWERMODE_HIGHSPEED I got bouncing signal (spikes, glitches) at the rising/falling edges of the comparator output. The max hysteresis is used.
The error is not large and consequent about 0.6 – 0.7Hz less: The standard deviation also large: 0.07Hz, is should be 0.002Hz.
Maybe the NUCLEO-114 runs from an RC oscillator, not crystal?
As far as I understand the CPU is clocked from HSE clock. It is MCO of STLINK-V3E which is 8MHz. Is this an RC oscillator or crystal? The other acceptable option would be the X3 25MHz crystal, but unfortunately it is not assembled...
Thanks,
Louis
