In other words, the output is an open or floating terminal that is neither a low nor a high. The Hi-Z state is a condition in which both transistors in the totem-pole arrangement are turned off so that the output terminal is a high impedance to ground and to V CC. The tristate logic circuit utilizes the high speed operation of the totem-pole arrangement while permitting outputs to be wiredANDed (connected together). Such circuits are called Tristate or three state logic. To overcome these difficulties, special circuits have been developed in which there is one more state of output, referred to as the third state or high impedance (Hi-Z) state, in addition to low and high states. This causes the problems of loading and operation speed.
Open collector outputs can be connected together with a common collector resistor connected externally.Totem-pole outputs cannot be connected together due to very large current drain from the supply and consequent heating of ICs which may get damaged.
