Circuit blocking codes or code groups in telephone equipment - differentiates between free and blocked code numbers by applying different potentials

摘要

The circuit enables codes or code groups in telephone instruments or PBXs to be blocked although allowing emergency calls to be made. Electronic bistable switches are tripped to their operating position when a certain code number is dialled, or a certain potential is applied by a mechanical or electromechanical device. The bistable element is so inserted into a gate pyramid, that the system differentiates between marked free and blocked code numbers, with different potentials applied when code numbers are marked free or blocked. Switches differentiate this marking by operation or non-operation of a relay. The marking is erased by resetting the bistable element by a mechanical device or a gate pyramid.