56.6.6.3 Changing the Duty-Cycle, the Period and the Dead-Times

It is possible to modulate the output waveform duty-cycle, period and dead-times.

To prevent unexpected output waveform, the user must use the PWM Channel Duty Cycle Update Register (PWM_CDTYUPDx), the PWM Channel Period Update Register (PWM_CPRDUPDx) and the PWM Channel Dead Time Update Register (PWM_DTUPDx) to change waveform parameters while the channel is still enabled.

  • If the channel is an asynchronous channel (SYNCx = 0 in PWM Sync Channels Mode Register (PWM_SCM)), these registers hold the new period, duty-cycle and dead-times values until the end of the current PWM period and update the values for the next period.
  • If the channel is a synchronous channel and update method 0 is selected (SYNCx = 1 and UPDM = 0 in PWM_SCM register), these registers hold the new period, duty-cycle and dead-times values until the bit UPDULOCK is written at ‘1’ (in PWM Sync Channels Update Control Register (PWM_SCUC)) and the end of the current PWM period, then update the values for the next period.
  • If the channel is a synchronous channel and update method 1 or 2 is selected (SYNCx = 1 and UPDM = 1 or 2 in PWM_SCM register):
    • registers PWM_CPRDUPDx and PWM_DTUPDx hold the new period and dead-times values until the bit UPDULOCK is written at ‘1’ (in PWM_SCUC) and the end of the current PWM period, then update the values for the next period.
    • register PWM_CDTYUPDx holds the new duty-cycle value until the end of the update period of synchronous channels (when UPRCNT is equal to UPR in PWM Sync Channels Update Period Register (PWM_SCUP)) and the end of the current PWM period, then updates the value for the next period.
      Note: If the update registers PWM_CDTYUPDx, PWM_CPRDUPDx and PWM_DTUPDx are written several times between two updates, only the last written value is taken into account.
Figure 56-35. Synchronized Period, Duty-Cycle and Dead-Time Update