5 PWM Triggering

The PWM module is based on triggers. Each cycle must have a trigger to generate a PWM cycle. PG1 is self-triggered and will run continuously. All other PGs get their SOC trigger from PG1 either directly or through another PG. There are two methods to trigger a SOC: Start Of Cycle Select (SOCS) and the sync instance of the PG Control Inputs (PCI).

The phase offsets used for 0°, 90°, 120° and 240° SOC triggers are implemented using TRIGy timers within the PG. These timer events are then utilized by trigger outputs. There are multiple types of trigger outputs that can be used for various purposes, including SOC triggers. They are named PGTRIGOUT, DACx TRIG, and ADCx TRIG. These triggers are then mapped to top-level PWM event outputs, PWMEVTA through PWMEVTD. These signals are then distributed to the other PGs' PCI inputs for their respective SOC event trigger. Figure 5-1 illustrates the SOC triggering scheme used in this example.

The following equations define the phase offsets used by the system. They are calculated and updated each time the period changes.

All PGs, except PG1, operate in re-triggerable mode. This allows a subsequent SOC trigger to start a new cycle when a cycle is already in progress, allowing the shortening of the period for frequency modulation. All PGs other than PG1 use a period of the maximum allowable value, which the PG should not reach in normal operation.