基于msp430f5529的ads1118采样问题，请问为什么我采不出我想要的 电压，以下是我的程序代码

#include "msp430.h"
#include "lcd12864p.h"
#include "main.h"
uchar str2[6]={0};
void ADS1118_GPIO_Init(void)
{ //P1OUT |= 0x02; // Set P1.0 for LED
// Set P1.1 for slave reset
// P1DIR |= 0x03; // Set P1.0-2 to output direction
P3SEL |= BIT3+BIT4; // P3.3,4 option select
P2SEL |= BIT7; // P2.7 option select
P2OUT |= BIT3; // Set P1.1 for CS
P2DIR |= BIT3; // Set P1.1 to output direction

}

/*
* Mode 0: Only write config register to ADS1118
* Mode 1: Write config register to ADS1118 as well as read data from ADS1118
*/
signed int ADS1118_WriteSPI(unsigned int config, unsigned char mode)
{
signed int msb;
unsigned int temp;
signed int dummy;

temp = config;
if (mode==1) temp = 0;
while (!(UCA0IFG&UCTXIFG));
UCA0TXBUF = (temp >> 8 ); // Write MSB of Config
while (!(UCA0IFG&UCRXIFG));
msb =UCA0RXBUF; // Read MSB of Data

while (!(UCA0IFG&UCTXIFG));
UCA0TXBUF = (temp & 0xff); // Write LSB of Config
while (!(UCA0IFG&UCRXIFG));
msb = (msb << 8) |UCA0RXBUF; // Read LSB of Data

while (!(UCA0IFG&UCTXIFG));
UCA0TXBUF = (temp >> 8 ); // Write MSB of Config
while (!(UCA0IFG&UCRXIFG));
dummy =UCA0RXBUF; // Read MSB of Config

while (!(UCA0IFG&UCTXIFG));
UCA0TXBUF = (temp & 0xff); // Write LSB of Config
while (!(UCA0IFG&UCRXIFG));
dummy = (dummy <<8) |UCA0RXBUF; // Read LSB of Config
__delay_cycles(100);
return msb;
}
void ADS1118_SPI_Init(void)
{
UCA0CTL0 |= UCMST+UCSYNC+UCCKPL+UCMSB; // 3-pin, 8-bit SPI master
// Clock polarity high, MSB
UCA0CTL1 |= UCSSEL_2; // SMCLK
UCA0BR0 = 0x02; // 2
UCA0BR1 = 0; //
UCA0MCTL = 0; // No modulation
UCA0CTL1 &= ~UCSWRST; // **Initialize USCI state machine**

__delay_cycles(100); // Wait for slave to initialize
}

void ADS1118_ADS_Config(signed int temp_config_value)
{
signed int Config_Value;

Config_Value = temp_config_value;

P2OUT &=~ BIT3; // Set CS low
__delay_cycles(100); // Wait for slave to initialize

ADS1118_WriteSPI(Config_Value,0); // Write configuration to ADS1118

__delay_cycles(100); // Wait for slave to initialize

P2OUT |= BIT3; // Set CS high
}

int ADS1118_ADS_read(void)
{
unsigned int Data, Config_Value;

Config_Value = 0;

P2OUT &=~ BIT3; // Set CS low
Data = ADS1118_WriteSPI(Config_Value,1); // read data from ADS1118
P2OUT |= BIT3; // Set CS high

return Data;
}

void main(void)
{
WDTCTL = WDTPW+WDTHOLD; // Stop watchdog timer
volatile int ADC_result;
float re;
ADS1118_GPIO_Init();
ADS1118_SPI_Init();
//ADS_Config();
Init_Lcd(); //LCD12864初始化
while(1)
{

ADS1118_ADS_Config(0xC3E3); //Only Select AIN1,860SPS,+-4.096V scan voltage range

ADC_result = ADS1118_ADS_read(); // read data from ch1,the last time result
re = ADC_result*1.0/32768*4.096;
LCD_WriteString(1, 0,"AD DA 测试"); //不使用printf();时lcd12864测试
LCD_WriteString(3, 0,"采样值:");
LCD_WriteString(4, 0,"A1:");
LCD_WriteString(3, 4, "%.4f",ADC_result);
LCD_WriteString(4, 4, "%.4f",re);
__delay_cycles(10000);
}
}