Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).
Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).
Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).
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Enhanced PWM (ePWM) Module www.ti.com<br />
<strong>15</strong>.2.2.5.3 Action-Qualifier Event Priority<br />
It is possible for the ePWM action qualifier to receive more than one event at the same time. In this case<br />
events are assigned a priority by the hardware. The general rule is events occurring later in time have a<br />
higher priority and software forced events always have the highest priority. The event priority levels for updown-count<br />
mode are shown in Table <strong>15</strong>-17. A priority level of 1 is the highest priority and level 7 is the<br />
lowest. The priority changes slightly depending on the direction of TBCNT.<br />
Table <strong>15</strong>-17. Action-Qualifier Event Priority for Up-Down-Count Mode<br />
Event if TBCNT is Incrementing Event if TBCNT is Decrementing<br />
Priority Level TBCNT = 0 up to TBCNT = TBPRD TBCNT = TBPRD down to TBCNT = 1<br />
1 (Highest) Software forced event Software forced event<br />
2 Counter equals CMPB on up-count (CBU) Counter equals CMPB on down-count (CBD)<br />
3 Counter equals CMPA on up-count (CAU) Counter equals CMPA on down-count (CAD)<br />
4 Counter equals zero Counter equals period (TBPRD)<br />
5 Counter equals CMPB on down-count (CBD) (1)<br />
6 (Lowest) Counter equals CMPA on down-count (CAD) (1)<br />
Counter equals CMPB on up-count (CBU) (1)<br />
Counter equals CMPA on up-count (CBU) (1)<br />
(1) To maintain symmetry for up-down-count mode, both up-events (CAU/CBU) and down-events (CAD/CBD) can be generated for<br />
TBPRD. Otherwise, up-events can occur only when the counter is incrementing and down-events can occur only when the<br />
counter is decrementing.<br />
Table <strong>15</strong>-18 shows the action-qualifier priority for up-count mode. In this case, the counter direction is<br />
always defined as up and thus down-count events will never be taken.<br />
Table <strong>15</strong>-18. Action-Qualifier Event Priority for Up-Count Mode<br />
Priority Level Event<br />
1 (Highest) Software forced event<br />
2 Counter equal to period (TBPRD)<br />
3 Counter equal to CMPB on up-count (CBU)<br />
4 Counter equal to CMPA on up-count (CAU)<br />
5 (Lowest) Counter equal to Zero<br />
Table <strong>15</strong>-19 shows the action-qualifier priority for down-count mode. In this case, the counter direction is<br />
always defined as down and thus up-count events will never be taken.<br />
Table <strong>15</strong>-19. Action-Qualifier Event Priority for Down-Count Mode<br />
Priority Level Event<br />
1 (Highest) Software forced event<br />
2 Counter equal to Zero<br />
3 Counter equal to CMPB on down-count (CBD)<br />
4 Counter equal to CMPA on down-count (CAD)<br />
5 (Lowest) Counter equal to period (TBPRD)<br />
1648 <strong>Pulse</strong>-<strong>Width</strong> <strong>Modulation</strong> <strong>Subsystem</strong> (<strong>PWMSS</strong>) SPRUH73E–October 2011–Revised May 2012<br />
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