Abstract:Abstrct: As a means of system testing and fault diagnosis and isolation, BIT (Built In Test) technology is widely used in avionics reliability, maintainability, testability and safety design. In this paper, according to the requirements of BIT test for an UAV airborne mission load and combining the composition and control function of the mission load control module and the type of BIT test signal is analyzed, a BIT detection circuit for single-port multi-state voltage based on A/D converter is presented, and a BIT detection method for single-port multi-state voltage based on diode switching characteristics is proposed, the results of simulation and flight test show that the circuit meets the requirements of volume reduction, energy saving,cost reduction and high reliability, and has been successfully applied to similar products of multi-type UAV.