Enhanced PWM (ePWM) Module
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15.2.2.4.1 Purpose of the Counter-Compare Submodule
The counter-compare submodule takes as input the time-base counter value. This value is continuously
compared to the counter-compare A (CMPA) and counter-compare B (CMPB) registers. When the time-
base counter is equal to one of the compare registers, the counter-compare unit generates an appropriate
event.
The counter-compare submodule:
• Generates events based on programmable time stamps using the CMPA and CMPB registers
– CTR = CMPA: Time-base counter equals counter-compare A register (TBCNT = CMPA).
– CTR = CMPB: Time-base counter equals counter-compare B register (TBCNT = CMPB)
• Controls the PWM duty cycle if the action-qualifier submodule is configured appropriately
• Shadows new compare values to prevent corruption or glitches during the active PWM cycle
15.2.2.4.2 Controlling and Monitoring the Counter-Compare Submodule
Table 15-13 lists the registers used to control and monitor the counter-compare submodule. Table 15-14
lists the key signals associated with the counter-compare submodule.
Table 15-13. Counter-Compare Submodule Registers
Acronym Register Description Address Offset Shadowed
CMPCTL Counter-Compare Control Register. Eh No
CMPAHR HRPWM Counter-Compare A Extension Register
(1)
10h Yes
CMPA Counter-Compare A Register 12h Yes
CMPB Counter-Compare B Register 14h Yes
(1)
This register is available only on ePWM modules with the high-resolution extension (HRPWM). On ePWM modules that do not
include the HRPWM, this location is reserved. See Section 15.1.2 to determine which ePWM instances include this feature.
Table 15-14. Counter-Compare Submodule Key Signals
Signal Description of Event Registers Compared
CTR = CMPA Time-base counter equal to the active counter-compare A value TBCNT = CMPA
CTR = CMPB Time-base counter equal to the active counter-compare B value TBCNT = CMPB
CTR = PRD Time-base counter equal to the active period. TBCNT = TBPRD
Used to load active counter-compare A and B registers from the shadow register
CTR = 0 Time-base counter equal to zero. TBCNT = 0000h
Used to load active counter-compare A and B registers from the shadow register
1512
Pulse-Width Modulation Subsystem (PWMSS) SPRUH73H–October 2011–Revised April 2013
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