Question

The answer is above but this is from an exam review and I need help understanding how to get that answer. Please provide steps as to how and why the answer is register 1 and 2. Thanks!

Q9. Suppose a certain temperature sensor (with a range of -100 to +100 degrees Celsius) measures data in 18-bit two's complement format and stores it across three registers in the following manner: X17 X16 X15 X14X13 X12 X11 0 Register 1 Register_2 Register3 where, XO is the least significant bit and X17 is the sign bit. Assume that the fifth and sixth bits of Register_2 (i.e. X8 and X7) are corrupted and always store '1' regardless of the temperature. Which register(s) should you read to obtain the minimum possible resolution (in terms of degrees Celsius)? What is this resolution? Registers 1 & 2 (ignore X8, X7, and X6) X17 to X9 X17 X16 X15 X14 X13 X12 X11 0 200 0.3906°c Register 1 Register_2 29

Answer 1

Solution:

The ADC is an 18 bit with 2 complement format

X17 represents Sign bit and X16--X0 represents magnitude.

Voltage input range = -100 to 100 = 200degC.

The effective bits to represent the analog value into digital = input range / 2^N

N - No of bits = 18

The registers contain the digitized signal with registers R1, R2 and R3

Register_2 contain bits from X10 - X6 values.

If the content of the register (X8 and X7) is stuck at '1' always, it is not possible to get the correct data with bits X6 to X0 also.

So, valid bits to represent the Analog input into digitized form is taken as X17 - X9 only.

No of bits = N = 9.

Resolution = input range / 2^N

Resolution = input range / 2⁹ = 0.390625degC