Decoder circuitry for selectively activating loads

Abstract

A decoder circuit for selectively activating external loads which finds particular utility in automatic garage door operators. The coincidence of a repeatedly received digital word code with an internally generated local code results in a matched signal, each of the matched signals being stored in an accumulator device. A free running oscillator is used to reset the accumulator if a predetermined number of successive clock pulses are generated without an intervening matched signal. If a given plurality of matched signals are received and stored in the accumulator before it is reset, the accumulator will provide an output signal to a latch which activates the load. Once set, the output latch will not be reset unless a subsequent given number of successive clock pulses are generated without an intervening matched signal. In such manner, the decoder circuitry accommodates a limited number of mismatches possibly due to interference while still maintaining significant security aspects of the decoder circuitry. The resetting of the output latch will not occur immediately upon the occurence of a subsequent mismatch but is delayed to prevent the double trip condition often encountered in the automatic garage door operator field.