Enhanced Pulse Width Modulator (ePWM) Reference Guide

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Z P Z P
TBCTR
EPWMxA
EPWMxB
CA CA
CB
CB
Action-Qualifier (AQ) Submodule
Figure 2-26. Up-Down-Count, Dual Edge Asymmetric Waveform, With Independent Modulation on
EPWMxA—Active Low
A PWM period = 2 × TBPRD × TBCLK
B Rising edge and falling edge can be asymmetrically positioned within a PWM cycle. This allows for pulse placement
techniques.
C Duty modulation for EPWMxA is set by CMPA and CMPB.
D Low time duty for EPWMxA is proportional to (CMPA + CMPB).
E To change this example to active high, CMPA and CMPB actions need to be inverted (i.e., Set ! Clear and Clear Set).
F Duty modulation for EPWMxB is fixed at 50% (utilizes spare action resources for EPWMxB)
Example 2-7 contains a code sample showing initialization and run time for the waveforms in Figure 2-26 .
Use the code in Example 2-1 to define the headers.
Example 2-7. Code Sample for Figure 2-26
// Initialization Time
// = = = = = = = = = = = = = = = = = = = = = = = =
EPwm1Regs.TBPRD = 600; // Period = 2 × 600 TBCLK counts
EPwm1Regs.CMPA.half.CMPA = 250; // Compare A = 250 TBCLK counts
EPwm1Regs.CMPB = 450; // Compare B = 450 TBCLK counts
EPwm1Regs.TBPHS = 0; // Set Phase register to zero
EPwm1Regs.TBCNT = 0; // clear TB counter
EPwm1Regs.TBCTL.bit.CTRMODE = TB_UPDOWN; // Symmetric
EPwm1Regs.TBCTL.bit.PHSEN = TB_DISABLE; // Phase loading disabled
EPwm1Regs.TBCTL.bit.PRDLD = TB_SHADOW;
EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_DISABLE;
EPwm1Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // TBCLK = SYSCLKOUT
EPwm1Regs.TBCTL.bit.CLKDIV = TB_DIV1;
EPwm1Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW;
EPwm1Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW;
EPwm1Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO; // load on CTR = Zero
EPwm1Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO; // load on CTR = Zero
EPwm1Regs.AQCTLA.bit.CAU = AQ_SET;
EPwm1Regs.AQCTLA.bit.CBD = AQ_CLEAR;
EPwm1Regs.AQCTLB.bit.ZRO = AQ_CLEAR;
EPwm1Regs.AQCTLB.bit.PRD = AQ_SET;
// Run Time
// = = = = = = = = = = = = = = = = = = = = = = = =
EPwm1Regs.CMPA.half.CMPA = EdgePosA; // adjust duty for output EPWM1A only
EPwm1Regs.CMPB = EdgePosB;
SPRU791D – November 2004 – Revised October 2007 ePWM Submodules 49
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