US Patent 7394729 Time constant based fixed parameter assignment

A method for assigning a value to a fixed parameter in an electrical device where the fixed parameter has multiple states includes associating a time value to each state of the fixed parameter, driving a first input terminal of the electrical device to a first voltage value, receiving an input ramp signal on the first input terminal where the input ramp signal has a first time constant value and a voltage magnitude that varies from the first voltage value to a second voltage value, comparing the voltage level of the input ramp signal to a threshold value, when the voltage level of the input ramp signal reaches the threshold value, determining the elapsed time from the driving of the first input terminal, and selecting a state for the fixed parameter based on the amount of elapsed time until the voltage level of the input ramp signal reaches the threshold level.