TI中文支持网Part Number:TMS320F28335
您好，在设置EPWM死区模块时，用示波器观察输出EPWM波形，发现如下现象。EPWM1A经过死区模块，但是不翻转，示波器观察的是正常波形。但其他条件不变，EPWM1经过死区模块，经过翻转，即配置DBCTL[POLSEL]模块，用示波器观察输出波形，发现EPWM1已经翻转，但翻转前有个短波，且为高电平，请问这一现象怎么解释。
Yale Li：
方便发一下配置代码和波形吗？
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ke Lan：
好的，EPWM代码如下：死区时间为0，频率为100khz.EPWM1和EPWM2配置一样，波形如链接所示，以EPWM1A的上升沿为触发，EPWM1B和EPWM2B在程序中设置了翻转，可以看到出发前有两个短波，而且EPWM1B比EPWM2B短波时间要长。
void Init_epwm1(void){
EPwm1Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up-down EPwm1Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; EPwm1Regs.TBCTL.bit.CLKDIV = TB_DIV1; EPwm1Regs.TBCTL.bit.PHSEN = TB_DISABLE; // Enable phase loading EPwm1Regs.TBCTL.bit.PRDLD = TB_SHADOW; // TBPRD is loaded from its shadow register
EPwm1Regs.TBPRD = EPWM_PRD; // Set timer period (100kHz) EPwm1Regs.TBPHS.half.TBPHS = 0x0000; // Phase is 0 EPwm1Regs.TBCTR = 0x0000; // Clear counter EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_CTR_ZERO; // 同步信号输出选择TBCTR=0 EPwm1Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW; // CMPA Shadow mode EPwm1Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO; // Load on CTR = 0 EPwm1Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW; // CMPA Shadow mode EPwm1Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO; // Load on CTR = 0
EPwm1Regs.CMPA.half.CMPA = 2*D* EPWM_PRD; // Initial duty
EPwm1Regs.AQCTLA.bit.CAU = AQ_CLEAR; // TBCTR = CMPA on Down Count：Clear EPwm1Regs.AQCTLA.bit.CAD = AQ_NO_ACTION; // TBCTR = CMPA on Up Count：NO ACTION EPwm1Regs.AQCTLA.bit.ZRO = AQ_SET; // TBCTR = 0 on Up Count：Set
EPwm1Regs.AQCTLB.bit.CAU = AQ_NO_ACTION; EPwm1Regs.AQCTLB.bit.CAD = AQ_CLEAR; EPwm1Regs.AQCTLB.bit.ZRO = AQ_SET; EPwm1Regs.DBCTL.bit.OUT_MODE = DB_FULL_ENABLE; //0x3 MODE2 AHC high level delay (AHC)死区双边使能 EPwm1Regs.DBCTL.bit.POLSEL = DB_ACTV_HIC; //0x2 A不反转，B反转 EPwm1Regs.DBCTL.bit.IN_MODE = DBA_RED_DBB_FED;
EPwm1Regs.DBRED = EPWM1_DBRED; EPwm1Regs.DBFED = EPWM1_DBFED; }
void Init_epwm2(void){
EPwm2Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up-down EPwm2Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; EPwm2Regs.TBCTL.bit.CLKDIV = TB_DIV1; EPwm2Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Enable phase loading EPwm2Regs.TBCTL.bit.PRDLD = TB_SHADOW; // TBPRD is loaded from its shadow register
EPwm2Regs.TBPRD = EPWM_PRD;
EPwm2Regs.TBPHS.half.TBPHS = 0; EPwm2Regs.TBCTR = 0x0000; // Clear counter EPwm2Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;
EPwm2Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW; // CMPA Shadow mode EPwm2Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO; // Load on CTR = 0 EPwm2Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW; // CMPA Shadow mode EPwm2Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO; // Load on CTR = 0
EPwm2Regs.CMPA.half.CMPA = 2*D* EPWM_PRD; // Initial duty EPwm2Regs.AQCTLA.bit.CAU = AQ_CLEAR; // TBCTR = CMPA on Down Count：Clear EPwm2Regs.AQCTLA.bit.CAD = AQ_NO_ACTION; // TBCTR = CMPA on Up Count：NO ACTION EPwm2Regs.AQCTLA.bit.ZRO = AQ_SET; // TBCTR = 0 on Up Count：Set
EPwm2Regs.AQCTLB.bit.CAU = AQ_NO_ACTION; EPwm2Regs.AQCTLB.bit.CAD = AQ_CLEAR; EPwm2Regs.AQCTLB.bit.ZRO = AQ_SET;
EPwm2Regs.DBCTL.bit.OUT_MODE = DB_FULL_ENABLE; //0x3 MODE2 AHC high level delay (AHC)死区双边使能 EPwm2Regs.DBCTL.bit.POLSEL = DB_ACTV_HIC; //0x2 A不反转，B反转 EPwm2Regs.DBCTL.bit.IN_MODE = DBA_RED_DBB_FED;
EPwm2Regs.DBRED = EPWM2_DBRED; EPwm2Regs.DBFED = EPWM2_DBFED;
}
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ke Lan：
抱歉刚才操作不当，波形如上图所示
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Yale Li：
请描述一下测量的操作步骤
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ke Lan：
1、示波器设定好触发，触发源为EPWM1A，触发电平如图设定为1.2V，且为上升沿触发。四个探头分为接DSP EPWM1A\1B\2A\2B对应的IO口。2、按下给DSP供电电源开关，接通开关，示波器即出现如上波形，捕捉到了第一个PWM波如图上所示。
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Yale Li：
能否把触发源设置为1B或者2B再观察一下？
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ke Lan：
把触发源设置为1B后，波形也是一样的。经过测试，1B和2B都经过翻转，如果配置1B和2B不进入死区翻转，第一个波就没有这个短波这个现象。配置为死区翻转后，才会有短波现象。所以考虑这种现象是死区的一种机制，来确保上下桥臂不会直通。
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Yale Li：
我需要一些时间来看一下
