Integrated Circuits Used 74LS138 Procedure Add IC 74LS138 into ICBase-3 (74LS138).Connect VCC Port to Pin-20 (VCC) of ICBase-3 (74LS138).Connect GND Port to Pin-8 (Ground) of ICBase-3 (74LS138).Connect Pin-3 (Input) of ICBase-3 (74LS138) to Input-2.