对28035 官方历程疑问

测试28035的官方历程epwm_timer_interrupts，有个疑问，贴出代码：

   EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;  // Pass through   

EPwm2Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;  // Pass through

   EPwm3Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;  // Pass through

   EPwm4Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;  // Pass through

我有个疑问，4个EPWM的同步源是什么，还有下面代码：

   EPwm1Regs.TBPHS.half.TBPHS = 100;

   EPwm2Regs.TBPHS.half.TBPHS = 200;

   EPwm3Regs.TBPHS.half.TBPHS = 300;  

  EPwm4Regs.TBPHS.half.TBPHS = 400;

4个EPWM在何时加载上述四个值，我对4个EPWM的同步源不是很清楚，望各位高手予以解答。