MC908QT1 FREESCALE [Freescale Semiconductor, Inc], MC908QT1 Datasheet - Page 125

• Manufacturer Part Number: MC908QT1
• Description: Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

14.4.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use the following
initialization procedure:
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIM channel
0 registers (TCH0H:TCH0L) initially control the buffered PWM output. TIM status control register 0
(TSCR0) controls and monitors the PWM signal from the linked channels. MS0B takes priority over MS0A.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIM overflows. Subsequent output
compares try to force the output to a state it is already in and have no effect. The result is a 0% duty cycle
output.
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100% duty
cycle output. See
14.5 Interrupts
The following TIM sources can generate interrupt requests:
Freescale Semiconductor
1. In the TIM status and control register (TSC):
2. In the TIM counter modulo registers (TMODH:TMODL), write the value for the required PWM
3. In the TIM channel x registers (TCHxH:TCHxL), write the value for the required pulse width.
4. In TIM channel x status and control register (TSCx):
5. In the TIM status control register (TSC), clear the TIM stop bit, TSTOP.
•
•
period.
TIM overflow flag (TOF) — The TOF bit is set when the TIM counter reaches the modulo value
programmed in the TIM counter modulo registers. The TIM overflow interrupt enable bit, TOIE,
enables TIM overflow CPU interrupt requests. TOF and TOIE are in the TIM status and control
register.
TIM channel flags (CH1F:CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIM CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE. Channel x TIM CPU interrupt requests are enabled when CHxIE =1.
CHxF and CHxIE are in the TIM channel x status and control register.
a. Stop the TIM counter by setting the TIM stop bit, TSTOP.
b. Reset the TIM counter and prescaler by setting the TIM reset bit, TRST.
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare
b. Write 1 to the toggle-on-overflow bit, TOVx.
c. Write 1:0 (polarity 1 — to clear output on compare) or 1:1 (polarity 0 — to set output on
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
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.
14.9.4 TIM Channel Status and Control
MC68HC908QY/QT Family Data Sheet, Rev. 5
NOTE
Registers.
Table
Table
14-3.
14-3.
Interrupts
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