Question -

What is Tri-state logic in 8085 microprocessor?

Explain three state gate.

A three state gate or tri-state logic is a digital circuit that exhibits three states, out of thee two of the states are signals equivalent to logic 1 and 0 as in a conventional gate. The third state is a high-impedance state. The high-impedance state behaves like an open circuit, which means that the output is disconnected and does not have a logic significance. Three-state gate may perform any conventional logic, such as AND or NAND.

The graphical symbol for three state buffer is shown below.


It is distinguished from a normal buffer by having both a normal input and a control input. The control input determines the output state.

When control input = 1
the output is enabled and gate behaves like any conventional buffer.

When control input =0
the output is disabled and gate goes to a high-impedance state regardless of the value in the normal input

The high-impedance state of a three-state fate provides a special feature not available in other gates.

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