The purpose is to provide a standard for 2.5 V nominal supply voltage logic devices for uniformity, multiplicity of sources, elimination of confusion, ease of device specification, and ease of use. This specification provides for compatibility between devices operating between either the Standard Range of 1.8 V to 2.7 V or the optional Extended Range of 1.65 V to 2.7 V supply voltages, as well as over-voltage tolerance with devices operating at 3.6 V.