Enhanced Pulse Width Modulator (ePWM) Reference Guide

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2.4.3 Action-Qualifier Event Priority
Action-Qualifier (AQ) Submodule
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 2-8 . 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 2-8. Action-Qualifier Event Priority for Up-Down-Count Mode
Priority Level Event If TBCTR is Incrementing Event If TBCTR is Decrementing
TBCTR = Zero up to TBCTR = TBPRD 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)
(1)
Counter equals CMPB on up-count (CBU)
(1)
6 (Lowest) Counter equals CMPA on down-count (CAD)
(1)
Counter equals CMPA on up-count (CBU)
(1)
(1)
To maintain symmetry for up-down-count mode, both up-events (CAU/CBU) and down-events (CAD/CBD) can be generated for
TBPRD. Otherwise, up-events can occur only when the counter is incrementing and down-events can occur only when the
counter is decrementing.
Table 2-9 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 2-9. 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 2-10 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 2-10. 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 2-11 .
ePWM Submodules40 SPRU791D – November 2004 – Revised October 2007
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