mc68hc908bd48 Freescale Semiconductor, Inc, mc68hc908bd48 Datasheet - Page 132

• Manufacturer Part Number: mc68hc908bd48
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Timer Interface Module (TIM)
10.5.4.1 Unbuffered PWM Signal Generation
Data Sheet
132
The value in the TIM counter modulo registers and the selected
prescaler output determines the frequency of the PWM output. The
frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIM counter modulo registers produces a PWM
period of 256 times the internal bus clock period if the prescaler select
value is 000 (see
The value in the TIM channel registers determines the pulse width of the
PWM output. The pulse width of an 8-bit PWM signal is variable in 256
increments. Writing $0080 (128) to the TIM channel registers produces
a duty cycle of 128/256 or 50%.
Any output compare channel can generate unbuffered PWM pulses as
described in
unbuffered because changing the pulse width requires writing the new
pulse width value over the old value currently in the TIM channel
registers.
An unsynchronized write to the TIM channel registers to change a pulse
width value could cause incorrect operation for up to two PWM periods.
For example, writing a new value before the counter reaches the old
value but after the counter reaches the new value prevents any compare
during that PWM period. Also, using a TIM overflow interrupt routine to
write a new, smaller pulse width value may cause the compare to be
missed. The TIM may pass the new value before it is written.
TCHx
OVERFLOW
Timer Interface Module (TIM)
10.5.4 Pulse Width Modulation
Figure 10-2. PWM Period and Pulse Width
PULSE
WIDTH
PERIOD
10.10.1 TIM Status and Control Register
COMPARE
OUTPUT
OVERFLOW
COMPARE
OUTPUT
(PWM). The pulses are
MC68HC908BD48
OVERFLOW
Freescale Semiconductor
(TSC)).
COMPARE
—
OUTPUT
Rev. 2.1