counter is not zero in step 576 control is transferred to the step 590 to test both the active and inactive time periods to determine whether they are less than 5 milliseconds if either is not less than 4 5 milliseconds then the radio state is cleared if not the bit counter is incremented control is then transferred to a step 582 to determine the difference between the active and inactive times a decision threshold of u00b1 0 768 milliseconds is then employed to determine if a bit is equal to zero one or two which is a determination as to what the state is of a particular trinary bit or three state bit having been received by the radio signal having determined the state of the trinary bit control is transferred to a step 594 where the storage value is multiplied by three in effect by doing a shift and the value of the trinary bit established in step 592 is then added control is transferred to a step 596 to determine the bit counter value if it is less than 11 control is transferred to a step 600 and the interrupt is returned from if it is greater.