Logics are generally binarydigital circuits that know two level states: High and Low or 1 and 0. However, there are also trinary logics that distinguish three states, the tri-state logics (3-state). Like the two-state logics, the tri-state logics have the states High and Low and, in addition, the state"high impedance", which is denoted by "Z".
The three logic states of a tri-state logic can be represented by the digits -1, 0, and 1, or alternatively by the digits 0, 1, and 2. In the trinary number system, each number consists of a combination of the digits 0, 1, and 2. The lowest digit corresponds to the logic state "untrue", the highest digit corresponds to the logic state "true", and the middle digit corresponds to the logic state "neutral". In the high state, the output level is pulled toward the positive supply voltage, while the low level is pulled toward ground. The third state represents an open, and therefore a high impedance output circuit. This state corresponds to that of an open, unconnected circuit.