Apparatus and method for detecting a digital change in data

摘要

In a DME system, the least significant decade of the present aircraft to ground station distance is maintained encoded in a memory, and an up-down counter maintains a variable count. The complement of the present distance is compared with the present count, and when a difference is detected, a logical pulse increments the counter and also indicates passage of the aircraft through another distance interval. The sense of the difference between the present distance and the count also is monitored, responsive to which the direction of the count is controlled.