The temperature register is unsigned. TEMP[13:0] = registers {0x12[5:0], 0x13[7:0]} . Full range of temperature sensor is 0 to 358 Kelvin (-273C to 85C). A 0x0000 reading from the two temp registers represents 0 Kelvin. The full scale reading from the two temperature registers (0x3FFF) should give 358 in Kelvin or 85 in degrees Celsius.