For a 3.3 V CMOS input,
- V_IH > 2 V
- V_IL < 0.8 V
Assuming the ADC scale is linear in voltage and is zero at 0V,
- 2V => 0x2FF (given) = 767
- 0.8 V => 0.8 / 2 * 767 = 307 = 0x133