Texas Instruments 28xxx 用户手册
www.ti.com
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.
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. 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.
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