28377例程中关于ADC的初始化问题

28377的例程中有下面一段代码，请问这个是干什么用的呢？

CpuSysRegs.PCLKCR13.bit.ADC_A = 1;//开启ADC时钟
CpuSysRegs.PCLKCR13.bit.ADC_B = 1;
CpuSysRegs.PCLKCR13.bit.ADC_C = 1;
CpuSysRegs.PCLKCR13.bit.ADC_D = 1;

//check if device is trimmed
if(*((Uint16 *)0x5D1B6) == 0x0000){
//device is not trimmed, apply static calibration values
AnalogSubsysRegs.ANAREFTRIMA.all = 31709;
AnalogSubsysRegs.ANAREFTRIMB.all = 31709;
AnalogSubsysRegs.ANAREFTRIMC.all = 31709;
AnalogSubsysRegs.ANAREFTRIMD.all = 31709;
}

CpuSysRegs.PCLKCR13.bit.ADC_A = 0;
CpuSysRegs.PCLKCR13.bit.ADC_B = 0;
CpuSysRegs.PCLKCR13.bit.ADC_C = 0;
CpuSysRegs.PCLKCR13.bit.ADC_D = 0;
EDIS;