The following registers configuration can be used to generate 20% of PWM duty cycle in up count mode.

EPWM_TBPRD = 62500
EPWM_TBCTL.CTRMODE = 0 → Up count mode
EPWM_TBCTL.CLKDIV = 1
EPWM_CMPA = 12500 (= 62500 x 20%)
EPWM_CMPCTL.SHDWAMODE = 0 → Shadow mode
EPWM_CMPCTL.LOADAMODE = 0 → Load on TBCNT = 0 when shadow mode is enabled.
EPWM_AQCTLA.CAU = 0x3 → Toggle EPWM output
EPWM_AQCTLA.ZRO = 0x2 → Force EPWM output HIGH

Then, there can be no unintended PWM duty cycle regardless the instance of writing a value into CMPA. Figure 5-1 is PWM signal probed when changing PWM duty cycle from 20% to 80%.

Figure 5-1 Probe PWM Changes With Shadow Mode in Up Count Mode

Figure 5-2 Analyze PWM Duty Cycle Change with Shadow Mode in Up Count Mode

This can be analyzed as in the following.

• Current duty cycle is 20%.
  Equation 9. $Duty = 100 \times \frac{12500}{12500 + 50000} = 20\%$
• Software writes 50000 into CMPA register in between ① and ②
• CMPA register is shadowed and is updated at TBCNT = 0.
• PWM toggles at the instance of ② when TBCNT = 0 and this makes duty cycle 80%.
  Equation 10. $Duty = 100 \times \frac{50000}{50000 + 12500} = 80\%$
• For the following PWM periods, PWM duty cycle stays at 80%.

This is just an example to show how to control PWM duty cycle especially for LED dimming without unintended brightness.