MC68HC908LB8_05 Datasheet, PDF (145/234 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Timebase
in Figure 15-4. Again, the timer modulus register is used to determine the maximum count. The PWM
period will equal:
(timer modulus) x (PWM clock period)
UP-ONLY COUNTER
MODULUS = 4
PWM = 0
PWM = 1
PERIOD = 4 X (PWM
CLOCK PERIOD)
PWM = 2
PWM = 3
PWM = 4
Figure 15-4. Edge-Aligned PWM (Positive Polarity)
15.3.2 Prescaler
To permit lower PWM frequencies, a prescaler is provided which will divide the PWM clock frequency by
1, 2, 4, or 8. Table 15-1 shows how setting the prescaler bits in PWM control register 2 affects the PWM
clock frequency. This prescaler is buffered and will not be used by the PWM generator until the LDOK bit
is set and a new PWM reload cycle begins.
MC68HC908LB8 Data Sheet, Rev. 1
Freescale Semiconductor
145