﻿ Tristate buffer floating output. Inverting symbol truth table.
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Tristate Inv Tristate Bus

Tristate buffer symbol, inverter and truth table

Inverting Tri-state buffer Truth Table, circuit and symbol below:

Tri state Buffer

In

ENA

Out

 ENA IN OUT 0 0 0 0 1 1 1 0 Z 1 1 Z
 ENA IN OUT2 0 0 1 0 1 0 1 0 Z 1 1 Z

Tri-state buffer with ENA low is switch open, Truth Table and symbol below:

 ENA IN OUT 0 0 Z 0 1 Z 1 0 0 1 1 1

Tri state Buffer

In

ENA

Out

Tri state Buffer

In

ENA

Out2

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Tri-state buffer with ENA High is Switch open or Hi-Z circuit. Truth Table and symbol are discussed below. First implementation of truth table allows the output to go floating without attaining a high or low. This allows other devices connected on shared bus to drive the bus.

Tri-state buffer acts as a switch in digital circuit by isolating a signal path in a circuit. This switch can attain three logical states. The three states are 0, 1 and ‘Z’. The logical state 0 and 1 are possible when the switch is CLOSE. The logical value ‘Z’ or high impedance is attained when switch is OPEN. So when switch is open the input to tristate buffer is isolated from the circuit and output can be driven by some other logical path on a shared connection/bus.

Verilog RTL example for tri-state logic buffer. Also discussed below are the output results.
Tristate buffer, inverting tristate buffer symbol, truth table and on chip implementations bus, bidirectional IO port direction control.

// Tristate Buffer

module tristate_buffer(input_x, enable, output_x);

input input_x;

input enable;

output output_x;

assign output_x = enable? input_x : 'bz;

endmodule

-----------------------------------------------------

Output of above Tri-State Buffer code

-----------------------------------------------------

input_x = 0, enable = 0, output_x = z

input_x = 1, enable = 0, output_x = z

input_x = 1, enable = 1, output_x = 1

input_x = 0, enable = 1, output_x = 0

(valid for most EDA flows)

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SystemVerilog