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18.3
Functional description
18.3.1
Timer/Counter control
The PWM has Start/Stop register. It controls start or stop of the Timer/Counter. If you set
this register, the Timer/Counter starts to run. If you reset this register, the Timer/Counter
stops immediately. Also there is a pause register. The pause register is used to stop
temporarily after one period. Although you set this register while the Timer/Counter is
running, the Timer/Counter will stop when the period ends.
The registers of PWM can be updated when it stops or pauses. Users cannot update the
registers while PWM is running.
18.3.2
Timer/Counter
The PWM has 8 Timer/Counter clocks, which can be divided by a prescaler. Each
Timer/Counter runs independently. The Timer/Counter is designed to count cycles of the
clocks or external input signal and generate interrupts when specified timer values are
occurred based on match register and limit register. The Timer/Counter can count up or
down.
The PWM has match registers and limit registers. The match registers control the duty cycle
of PWM output waveform. The limit registers control the period of the PWM output
waveform. The Timer/Counter becomes 0 when it reaches value of the limit register. If
PDMR(Periodic Mode Register) is set, the Timer/Counter counts repeatedly and if PDMR is
reset, the Timer/Counter stops counting.
Match register should be smaller than limit register(LR). If not, match interrupt is not
occurred and PWM output waveform is always 1.
Repetition mode
The Timer/Counter has two repetition mode: periodic and one-shot mode. In periodic mode,
the Timer/Counter recycles and then restarts when the Timer/Counter reaches the value of
limit register. Figure 26 shows periodic mode timing diagram.
PWMCLK
Prescale
1
2
Counter
Timer/Counter
10
Overflow
Interrupt
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