TM4C1294中ADC接口采样值跟实际的值相差大概1.2倍左右

通过配置好ADC接口后，用查询或中断方式进行采样，但是采样的值跟实际的值相差大概1.2倍左右。是初始化程序问题还是哪里需要做进一步设置？
初始化代码：
void ADC0Init(void)
[

ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);

GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_2 | GPIO_PIN_3);

ADCReferenceSet(ADC0_BASE, ADC_REF_EXT_3V);

ADCSequenceConfigure(ADC0_BASE, 1, ADC_TRIGGER_PROCESSOR, 0);

ADCSequenceStepConfigure(ADC0_BASE, 1, 0, ADC_CTL_CH0);

ADCSequenceStepConfigure(ADC0_BASE, 1, 1, ADC_CTL_CH1 | ADC_CTL_IE | ADC_CTL_END);

ADCSequenceEnable(ADC0_BASE, 1);

// ADCIntEnable(ADC0_BASE,1);
//
// IntEnable(INT_ADC0SS1);

ADCIntClear(ADC0_BASE, 1);
]

查询采样代码：
uint32_t *GetSampleADc(void)
[
uint32_t pui32ADC0Value[2] = [0];
uint32_t *ADC0Value = &pui32ADC0Value[0];

ADCProcessorTrigger(ADC0_BASE, 1);

while(!ADCIntStatus(ADC0_BASE, 1, false))
[
]

ADCIntClear(ADC0_BASE, 1);

ADCSequenceDataGet(ADC0_BASE, 1, pui32ADC0Value);

SysCtlDelay(g_ui32SysClock / 12);

return ADC0Value;
]