C5515 channel 2 read error after setting reserved bit 2

Hi,

We are using C5515. We are applying a 1.04V input to GPAIN0. Its a divided voltage from a battery of 4.2V (Divider resistances of 10k and 3.3k). We enabled Channel 2 by setting the reserved bit 2 of the SARPINCTRL register .

My reference voltage set to 1.3V ANA_LDO . I am getting a voltage value of 0.89V ie a count of 704 . When I measure the input pin voltage it is 1.041V. I even tried setting the multichannel mode from normal mode. Even then the result is the same . Its a 30% error.

How to over come this where am I making the error . ??

ADC code

SAR_PINCTRL = 0x3104;

SAR_CTRL = 0xAC00;

while (SAR_DATA & ADC_BUSY);

Sar = SAR_DATA;

SAR_PINCTRL = 0x3104;

return (Sar & 0x3ff);

all the above observations were performed using

SARGPOCTRL = 0x00E0;

when  SARGPOCTRL = 0x0000 then the count value read is 1023 for the same input.