Tristate gate

What is a tristate gate ？

Tristate means that its output can be general binary logical circuit , I.e. normal high level （ Logic 1） Or low level （ Logic 0）, It can also maintain a unique high impedance state . The high resistance state is equivalent to the isolation state （ The resistance is very high , It's the equivalent of an open circuit ）.

 

One in memory Storage unit , When the read-write control line is at low potential , The storage unit is opened , You can write ; When at high potential , You can read , But don't read or write , Use high resistance , At this time, the node is suspended （ Not pulled VDD perhaps GND） The state of , There is no circuit to drive him . High level , The low level can be pulled up and down by the internal circuit . and High resistance state The resistance of the pin to ground is infinite , At this time, the real level value can be read when reading the pin level .

application ：

If your device port is going to be on a bus , It has to go through the tristate buffer . Because only one port can be output on a bus at the same time , At this time, other ports must be High resistance state , At the same time, you can input the data of this output port . So you also need to have bus control management , Which port to access , Only the tri state buffer of that port can be transferred to the output state . This is a typical three state gate application .