Why will the conversion resolution drop if a port input instruction is executed during conversion?
The amplitude of digital signals is larger than that of analog signals, and therefore digital signals affect surrounding circuits. In the case of just digital signals, even if the noise generated is large, there is no negative effect as long as the threshold voltage is not exceeded. However, in the case of analog signals, there is a direct effect on the surrounding circuits equivalent to the amount of noise generated. The accuracy of A/D conversion therefore drops due to the noise from the digital signals.