Enhanced PWM (ePWM) Module
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
lists the registers used to control and monitor the counter-compare submodule.
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
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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