ads1247在温度升至50℃左右后读取的值为何是负数？

配置：

    WriteReg_S(Reg_MUX0|0x40, 0x00, 0x08);                    // Negative input  AIN0   Positive input   AIN1
    WriteReg_S(Reg_VBias|0x40, 0x00, 0x00);                   // Bias voltage not enabled (default) 
    WriteReg_S(Reg_MUX1|0x40, 0x00, 0x30);                    // Onboard reference selected   Internal reference is always on
    WriteReg_S(Reg_SYS0|0x40, 0x00, 0x59);                    // 2000SPS   the gain of the PGA 32
    WriteReg_S(Reg_IDAC0|0x40, 0x00, 0x06);                   // current source that can be used for sensor excitation  1000μA

当温度升到50摄氏度左右时，数据立马变为负值，当温度恢复为常温时测值又恢复正常。A0和A1输入端电压是正确的。仿真程序，发现从ADS1247返回的值确实是负值。