Integrated Circuits Used 74LS20 74LS139 Procedure Add IC 74LS20 into ICBase-2 (74LS20).Connect VCC Port to Pin-20 (VCC) of ICBase-2 (74LS20).Connect GND Port to Pin-7 (Ground) of ICBase-2 (74LS20).Add IC 74LS139 into ICBase-4 (74LS139).