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SPRUI07–March 2020
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Enhanced Pulse Width Modulator (ePWM) Module
3.2.4.3 Action-Qualifier Event Priority
It is possible for the ePWM action qualifier to receive more than one event at the same time. In this case
events are assigned a priority by the hardware. The general rule is events occurring later in time have a
higher priority and software forced events always have the highest priority. The event priority levels for up-
down-count mode are shown in Table 3-9. A priority level of 1 is the highest priority and level 7 is the
lowest. The priority changes slightly depending on the direction of TBCTR.
Table 3-9. Action-Qualifier Event Priority for Up-Down-Count Mode
Priority Level Event If TBCTR is Incrementing
TBCTR = Zero up to TBCTR = TBPRD
Event If TBCTR is Decrementing
TBCTR = TBPRD down to TBCTR = 1
1 (Highest) Software forced event Software forced event
2 Counter equals CMPB on up-count (CBU) Counter equals CMPB on down-count (CBD)
3 Counter equals CMPA on up-count (CAU) Counter equals CMPA on down-count (CAD)
4 Counter equals zero Counter equals period (TBPRD)
5 Counter equals CMPB on down-count (CBD) Counter equals CMPB on up-count (CBU)
6 (Lowest) Counter equals CMPA on down-count (CAD) Counter equals CMPA on up-count (CBU)
Table 3-10 shows the action-qualifier priority for up-count mode. In this case, the counter direction is
always defined as up and thus down-count events will never be taken.
Table 3-10. Action-Qualifier Event Priority for Up-Count Mode
Priority Level Event
1 (Highest) Software forced event
2 Counter equal to period (TBPRD)
3 Counter equal to CMPB on up-count (CBU)
4 Counter equal to CMPA on up-count (CAU)
5 (Lowest) Counter equal to Zero
Table 3-11 shows the action-qualifier priority for down-count mode. In this case, the counter direction is
always defined as down and thus up-count events will never be taken.
Table 3-11. Action-Qualifier Event Priority for Down-Count Mode
Priority Level Event
1 (Highest) Software forced event
2 Counter equal to Zero
3 Counter equal to CMPB on down-count (CBD)
4 Counter equal to CMPA on down-count (CAD)
5 (Lowest) Counter equal to period (TBPRD)
It is possible to set the compare value greater than the period. In this case the action will take place as
shown in Table 3-12.
Table 3-12. Behavior if CMPA/CMPB is Greater than the Period
Counter Mode Compare on Up-Count Event
CAU/CBU
Compare on Down-Count Event
CAD/CBD
Up-Count Mode If CMPA/CMPB ≤ TBPRD period, then the event
occurs on a compare match (TBCTR=CMPA or
CMPB).
Never occurs.
If CMPA/CMPB > TBPRD, then the event will not
occur.
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