mc68hc908jb8 Freescale Semiconductor, Inc, mc68hc908jb8 Datasheet - Page 186

• Manufacturer Part Number: mc68hc908jb8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Timer Interface Module (TIM)
11.5.4.3 PWM Initialization
Technical Data
186
NOTE:
NOTE:
In buffered PWM signal generation, do not write new pulse width values
to the currently active channel registers. User software should track the
currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as
generating unbuffered PWM signals.
To ensure correct operation when generating unbuffered or buffered
PWM signals, use this initialization procedure:
In PWM signal generation, do not program the PWM channel to toggle
on output compare. Toggling on output compare prevents reliable 0%
duty cycle generation and removes the ability of the channel to self-
correct in the event of software error or noise. Toggling on output
compare can also cause incorrect PWM signal generation when
changing the PWM pulse width to a new, much larger value.
1. In the TIM status and control register (TSC):
2. In the TIM counter modulo registers (TMODH:TMODL), write the
3. In the TIM channel x registers (TCHxH:TCHxL), write the value for
4. In TIM channel x status and control register (TSCx):
5. In the TIM status control register (TSC), clear the TIM stop bit,
value for the required PWM period.
the required pulse width.
TSTOP.
a. Stop the TIM counter by setting the TIM stop bit, TSTOP.
b. Reset the TIM counter and prescaler by setting the TIM reset
a. Write 0:1 (for unbuffered output compare or PWM signals) or
b. Write 1 to the toggle-on-overflow bit, TOVx.
c. Write 1:0 (to clear output on compare) or 1:1 (to set output on
bit, TRST.
1:0 (for buffered output compare or PWM signals) to the
mode select bits, MSxB:MSxA. (See
compare) to the edge/level select bits, ELSxB:ELSxA. The
output action on compare must force the output to the
complement of the pulse width level. (See
Timer Interface Module (TIM)
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
Table
Freescale Semiconductor
Table
11-3.)
11-3.)