Interfacing PIC Microcontrollers

resistors in series this becomes V = I(R

1

⫹R

2

). The power dissipated in the re-

sistor is given by P = IV. For AC signals, RMS voltages are used so that the

same model can be applied. Reactive components need the frequency of the

signal to be included, so V = IX is used, where X is the reactance. For a capac-

itor, the magnitude of the reactance is 1/ωC, for an inductor ωL, where C is the

capacitance and L the inductance. We then need to model the phase relation-

ship between voltage and current, using complex numbers, and so on.

Digital circuits are in principle easier, since they are modelled using simple

logical relationships, such as A = B.C, w