In this blog, we present a component called a tristate buffer. A Tri-State buffer is the integral component of random access memory as well as for communication between components such as registers.

What is Tristate Buffer?

The tristate buffer is drawn with one data input bit. One control input bit. One output bit and is described by this truth table.

The capital C here symbolizes high impedance or resistance, So very little current will pass through the buffer. The control bit of the tristate buffer acts as a valve that shuts current on and off from the circuit.

How it Works?

• Control bit Set to 1: When the control bit as one input voltage of the buffer is sent to the output.

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• Control bit Set to 0: The buffer will become a high impedance circuit and negligible current will flow through the circuit.

At this point, I want to address a common misconception that 0 volts output from a gate means that nothing is output from the gate. Current will always flow your circuit regardless of the voltage. But if the impedance is great enough that current will stop. So remember the current is flowing through a circuit when the output is 0 1. But No current is flowing through a circuit when the tristate buffer is a high impedance circuit.

Tri-State Buffer as a Multiplexer?

We can use tristate buffers much like how it is multiplexers. In a multiplexer, we use a selected to choose which data input value and send it to the output.

Analogously. We can use the tristate buffers control bit to select which data input value. Is allowed to pass to the output.

However. If you make a mistake in the design of the tristate buffer selection circuit. The results are much more catastrophic than a mistake in the design of a multiplexer. It’s too tristate buffers are enabled at the same time. We could damage the circuit.

To illustrate why this happens we need to remove the digital obstruction and look at the voltages and currents. If 2 components are put to the same wire transmitted from voltages. The current in the system will be governed by the resistance and the wire and the difference in voltage. Because there is a sense of a wire is essentially 0. The components will try to draw infinite current. This type of current draw can damage our circuits.

To summarize the tristate buffer is essentially a current valve that can shut off the output from specific components. The tristate buffer allows us to select one output for many descend to a wire or bus they must make absolutely certain that 2 components do not transmit the same wire bus.