Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).

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Enhanced PWM (ePWM) Module www.ti.com 15.2.2.4 Counter-Compare (CC) Submodule Figure 15-17 illustrates the counter-compare submodule within the ePWM. Figure 15-18 shows the basic structure of the counter-compare submodule. EPWMxSYNCI EPWMxSYNCO CTR = PRD CTR =0 Time-Base (TB) Counter Compare (CC) Time Base (TB) Module CMPCTL[LOADAMODE] CTR = PRD CTR = 0 Shadow load Shadow load CMPCTL[LOADBMODE] Figure 15-17. Counter-Compare Submodule CTR = PRD CTR = 0 CTR_Dir CTR = CMPA CTR = CMPB Action Qualifier (AQ) EPWMxA EPWMxB Interrupt controller TBCNT CTR = PRD CTR = 0 CTR = CMPA CTR = CMPB Dead Band (DB) CMPA CTR_Dir PWMchopper (PC) CTR = 0 EPWMxTZINT 16 16 CMPA Compare A Active Reg. CMPA Compare A Shadow Reg. TBCNT CMPB 16 16 Event Trigger and Interrupt (ET) Trip Zone (TZ) EPWMxINT EPWMxA EPWMxB TZ1 to TZn Figure 15-18. Counter-Compare Submodule Signals and Registers CMPB Compare B Active Reg. CMPB Compare B Shadow Reg. CTR = CMPA Digital comparator A CMPCTL [SHDWAFULL] CMPCTL [SHDWAMODE] CTR = CMPB Digital comparator B Interrupt controller Action Qualifier (AQ) Module CMPCTL[SHDWBFULL] GPIO MUX CMPCTL[SHDWBMODE] 1640 Pulse-Width Modulation Subsystem (PWMSS) SPRUH73E–October 2011–Revised May 2012 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated
www.ti.com 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 timebase 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 SPRUH73E–October 2011–Revised May 2012 Pulse-Width Modulation Subsystem (PWMSS) Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated 1641
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Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).

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