You will need to tell us more about your project.
Do you want to implement the 'deadband' in software or in hardware? What output switching device are you controlling? What output would you expect to see during the 'deadband' ?
Very simply, when the input value is above the high threshold value, you set the output to state A. When the input value is below the low threshold value, you set the output to state C. For other values of input, you are in the 'deadband' and must set the output to state B, but exactly what you do in software will depend on the device you are controlling.
I guess you are not trying to implement hysteresis, which has only two output states.