MC68HC908AS60ACFN FREESCALE [Freescale Semiconductor, Inc], MC68HC908AS60ACFN Datasheet - Page 233

• Manufacturer Part Number: MC68HC908AS60ACFN
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

20.3.4.3 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 TIMB channel
0 registers (TBCH0H–TBCH0L) initially control the buffered PWM output. TIMB status control register 0
(TBSC0) 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 TIMB 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
Freescale Semiconductor
1. In the TIMB status and control register (TBSC):
2. In the TIMB counter modulo registers (TBMODH–TBMODL) write the value for the required PWM
3. In the TIMB channel x registers (TBCHxH–TBCHxL) write the value for the required pulse width.
4. In TIMB channel x status and control register (TBSCx):
5. In the TIMB status control register (TBSC) clear the TIMB stop bit, TSTOP.
period.
a. Stop the TIMB counter by setting the TIMB stop bit, TSTOP.
b. Reset the TIMB counter and prescaler by setting the TIMB 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 (to clear output on compare) or 1:1 (to set output on compare) to the edge/level
or PWM signals) to the mode select bits, MSxB–MSxA (see
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.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
20.8.4 TIMB Channel Status and Control
NOTE
Table
Registers).
20-2).
Table
20-2).
Functional Description
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