M.o.s. input circuit with t. t. l. compatability

Claim 1

An interface circuit for coupling between a first logic stage having a first range of output signal levels and a second logic stage employing input signal levels different than said first stage output signal levels, said interface circuit comprising an input node for coupling to the output of the first logic stage and an output node for coupling to the input of the second logic stage, a voltage line at a level corresponding to one of the second logic stage signal levels, switching means having a control element and an output circuit coupled between said voltage line and said input node and effective when conductive to establish said output node at a first logic level, and when nonconductive to establish said output node at a second logic level, and control means coupled to said input node for controlling the conductive state of said switching means, said control means comprises second switching means having a control element coupled to said input node and an output circuit coupled to said voltage line and to the control element of said first named switching means, said output node being coupled to the output circuit of said second switching means and the control element of said first switching means.