在这个实例中，我固定给EPWM模块的TBPRD寄存器一个值，比如说400，但是用ECAP reference中的example3 中所示的代码捕获：
// Code snippet for CAP mode Delta Time, Rising edge trigger // Initialization Time //======================= // ECAP module 1 config ECap1Regs.ECCTL1.bit.CAP1POL = EC_RISING; ECap1Regs.ECCTL1.bit.CAP2POL = EC_RISING; ECap1Regs.ECCTL1.bit.CAP3POL = EC_RISING; ECap1Regs.ECCTL1.bit.CAP4POL = EC_RISING; ECap1Regs.ECCTL1.bit.CTRRST1 = EC_DELTA_MODE; ECap1Regs.ECCTL1.bit.CTRRST2 = EC_DELTA_MODE; ECap1Regs.ECCTL1.bit.CTRRST3 = EC_DELTA_MODE; ECap1Regs.ECCTL1.bit.CTRRST4 = EC_DELTA_MODE; ECap1Regs.ECCTL1.bit.CAPLDEN = EC_ENABLE; ECap1Regs.ECCTL1.bit.PRESCALE = EC_DIV1; ECap1Regs.ECCTL2.bit.CAP_APWM = EC_CAP_MODE; ECap1Regs.ECCTL2.bit.CONT_ONESHT = EC_CONTINUOUS; ECap1Regs.ECCTL2.bit.SYNCO_SEL = EC_SYNCO_DIS; ECap1Regs.ECCTL2.bit.SYNCI_EN = EC_DISABLE; ECap1Regs.ECCTL2.bit.TSCTRSTOP = EC_RUN; // Allow TSCTR to run // Run Time ( e.g. CEVT1 triggered ISR call) //========================================== // Note: here Time-stamp directly represents the Period value. Period4 = ECap1Regs.CAP1; // Fetch Time-Stamp captured at T1 Period1 = ECap1Regs.CAP2; // Fetch Time-Stamp captured at T2 Period2 = ECap1Regs.CAP3; // Fetch Time-Stamp captured at T3 Period3 = ECap1Regs.CAP4; // Fetch Time-Stamp captured at T4
period1/period2/period3/period4始终比TBPRD中的值大4，无论TBPRD中的值改成多少，捕获的值都有这个情况，
请问这是什么原因造成的？
