Three-state logic
From Wikipedia, the free encyclopedia
- See also: Tri-state area, tripoint.
In electronics a three-state, tri-state or 3-state digital logic gate is one in which the output circuit can be disconnected from the rest of the circuit, putting the output in a high impedance state. The output asserts neither a logical high nor logic low voltage level and, aside from stray capacitance and leakage currents, does not affect circuits connected to the output. Such output circuits are commonly used for input pins on integrated circuits, or when many devices must share a common bus, such as for memory or input/output circuit boards.
A common synonym is tristate logic, which is a registered trademark of National Semiconductor.
3-state outputs are implemented in various families of digital integrated circuits such as the Texas Instruments 7400 series of TTL gates, and often in the data and address bus lines of microprocessors.
This form of gate should not be confused with 3-value logic (ternary logic).
Tri-state logic is often used in transceiver applications, where it is necessary to connect from 8-bit SRAM to 16-bit SRAM, as on the 80C186XL processor.
