TMS320F28377D: 28377D DAC配置和信号输出

想用DSP自带的DAC输出，进行了如下配置：

EALLOW;
//write configurations
DacaRegs.DACCTL.bit.LOADMODE =1;
DacbRegs.DACCTL.bit.LOADMODE =1;

DacaRegs.DACCTL.bit.DACREFSEL =1;
DacbRegs.DACCTL.bit.DACREFSEL =1;

DacaRegs.DACCTL.bit.SYNCSEL =0; //PWM1信号更新
DacbRegs.DACCTL.bit.SYNCSEL =0;

DacaRegs.DACOUTEN.bit.DACOUTEN =1;
DacbRegs.DACOUTEN.bit.DACOUTEN =1;

//delay for 1ms to allow ADC time to power up
DELAY_US(1000);
EDIS;

通过修改影子寄存器值 无法输出相应的电压