Tri-state buffer logic symbol

Three-state buffer (Three-state Buffer) is also called a three-state gate and a three-state driver. Its three-state output is controlled by the enable input. When the enable input is valid, the device realizes normal logic state output (logic 0, logic 1); When the enable input is invalid, the output is in a high-impedance state, which is equivalent to being disconnected from the connected circuit.

Tri-state buffer logic symbol

Tri-state buffer function

In order to reduce the number of information transmission lines, most computers use bus transmission. That is, the same type of information all travels through the same set of transmission lines, and the information is transmitted in a time-sharing manner. There are generally three types of buses in computers: data bus, control bus, and address bus. In order to prevent information from interfering with each other, it is required that all transmission ends hanging on registers or memories on the bus can not only display two states of 0 and 1, but also another state - high impedance state x (at this time their The output is like being cut off and has no effect on the bus status. At this time, other devices can occupy the bus). Tri-state buffers can perform the above functions.

The role of tri-state buffer

The tri-state buffer not only has input and output ports, but also a control port.

When the control terminal EA = 1, output = input, the bus is driven by the device, and the data on the bus is the data on the input terminal;

When the control terminal EA = 0, the output terminal is in a high impedance state and the device has no driving effect on the bus.

When the output of the register is connected to a tri-state gate and the output of the tri-state gate is connected to the bus, a tri-state buffer is formed.

Tri-state buffers include unidirectional buffers and bidirectional buffers. Bidirectional buffers are mainly used for bidirectional ports and are often used in the construction of bidirectional data buses.