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2.3.1 Purpose of the Counter-Compare Submodule
2.3.2 Controlling and Monitoring the Counter-Compare Submodule
TBCTR[15:0]
Time
Base
(TB)
Module
16
CMPA[15:0]
16
16
16
CMPA
Compare A Active Reg.
CTR = CMPA
CTR = CMPB
Action
Qualifier
Module
Digital
comparator B
CMPB[15:0]
TBCTR[15:0]
CTR = PRD
CTR =0
CMPCTL[LOADAMODE]
Shadow
load
CTR = PRD
CTR = 0
CMPCTL[LOADBMODE]
CMPCTL[SHDWBFULL]
CMPCTL[SHDWBMODE]
CMPCTL
[SHDWAFULL]
CMPCTL
[SHDWAMODE]
CMPA
Compare A Shadow Reg.
Digital
comparator A
CMPB
Compare B Active Reg.
CMPB
Compare B Shadow Reg.
Shadow
load
(AQ)
Counter-Compare (CC) 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:
•
Generates events based on programmable time stamps using the CMPA and CMPB registers
–
CTR = CMPA: Time-base counter equals counter-compare A register (TBCTR = CMPA).
–
CTR = CMPB: Time-base counter equals counter-compare B register (TBCTR = 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
The counter-compare submodule operation is controlled and monitored by the registers shown in
Table 2-4
:
Table 2-4. Counter-Compare Submodule Registers
Register Name
Address Offset
Shadowed
Description
CMPCTL
0x0007
No
Counter-Compare Control Register.
CMPAHR
0x0008
Yes
HRPWM Counter-Compare A Extension Register
(1)
CMPA
0x0009
Yes
Counter-Compare A Register
CMPB
0x000A
Yes
Counter-Compare B Register
(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. This register is described in the
TMS320x28xx, 28xxx High-Resolution Pulse
Width Modulator (HRPWM) Reference Guide
(SPRU924). Refer to the device specific data manual to determine which ePWM
instances include this feature.
Figure 2-12. Detailed View of the Counter-Compare Submodule
SPRU791D – November 2004 – Revised October 2007
ePWM Submodules
33
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Summary of Contents for 28xxx
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