Tri-State Buffer

Truth table for a tri-state buffer
Enable InputInput AOutput
falsefalsehi-Z
falsetruehi-Z
truefalsefalse
truetruetrue

A tri-state buffer is similar to a buffer, but it adds an additional "enable" input that controls whether the primary input is passed to its output or not. If the "enable" inputs signal is true, the tri-state buffer behaves like a normal buffer. If the "enable" input signal is false, the tri-state buffer passes a high impedance (or hi-Z) signal, which effectively disconnects its output from the circuit.

Tri-state buffers are often connected to a bus which allows multiple signals to travel along the same connection.

The truth table for a tri-state buffer appears to the right.

Symbols

The symbol below can be used to represent a tri-state buffer.

Tri-State Buffer
Tri-State Buffer symbol

Live Example

Try the following interactive example to see for yourself how a tri-state buffer behaves.

Further Reading

To learn more, check out the following external resources:

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