Tri-State and Open Collector
another way to connect multiple gates to the same output wire
gate only has the ability to pull its output low; it cannot actively
this is done by pulling the wire up to a logic 1 voltage through a
If A and B are "1", output is actively pulled low
if C and D are "1", output is actively pulled low
if one gate is low, the other high, then low wins
if both gates are "1", the output floats, pulled
Hence, the two NAND functions are AND'd