Texas Instruments 28xxx Purpose of the Counter-Compare Submodule, Register Name Address Offset

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Counter-Compare (CC) Submodule

2.3.1 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:

∙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

2.3.2Controlling and Monitoring the Counter-Compare Submodule

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

	Time	TBCTR[15:0]	16
	Base
	(TB)
	Module		16
		CMPA[15:0]
CTR￿=￿PRD	Shadow	CMPA
CTR￿=0	load	Compare￿A￿Active￿Reg.
		CMPA
		Compare￿A￿Shadow￿Reg.
CMPCTL[LOADAMODE]		TBCTR[15:0]	16
		CMPB[15:0]	16

		Shadow
CTR￿=￿PRD			CMPB
		load
			Compare￿B￿Active￿Reg.
	CTR￿=￿0
			CMPB
			Compare￿B￿Shadow￿Reg.

	CTR￿=￿CMPA
Digital
comparator￿A
	CMPCTL
[SHDWAFULL]		Action
	CMPCTL	Qualifier
		(AQ)
[SHDWAMODE]
		Module

CTR￿=￿CMPB

Digital comparator￿B

CMPCTL[SHDWBFULL]

CMPCTL[SHDWBMODE]

CMPCTL[LOADBMODE]

SPRU791D–November 2004–Revised October 2007 ePWM Submodules 33

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