a microcomputer having a signal generating circuit which generates pulse width modulation signals defined by a carrier wave , and which controls controlled portions according to pulse width modulating signals . the signal generating circuit comprises a carrier wave defining timer which outputs a value varying the same as a waveform providing a carrier wave , a control register which controls the time period of the timer , a reload register which holds a count value , control blocks which generate pulse width modulation signals according to the value of the timer and the count value of the reload register .