Circuit with dual-purpose terminal

Abstract

A complementary MOS input circuit not only transfers input signal swinging between conventional logic levels in a normal mode but also provides a control signal upon application of an input signal swinging outside the normal range of logic levels. This control signal is then available to be used to change selective connections in an integrated circuit to change its operating function, for example. The input circuit includes first and second complementary MOS transistors arranged like an inverter but having their gates connected to a fixed potential and having input signal potential applied to the source of the first transistor. The transistors exhibit an output signal at the interconnection between their drain electrodes which output changes state on an input swinging past the fixed potential sufficiently to render the first transistor conductive.