Position: Index > Unclassified >

How does tri-state buffers work

2017-12-21 22:39  
Declaration:We aim to transmit more information by carrying articles . We will delete it soon, if we are involved in the problems of article content ,copyright or other problems.

Those who work with microcontrollers probably know about data buses. Only one device(memory, peripherals), that are connected to bus can work at one moment. So only one unit can have direct connection to bus besides CPU which usually is a host. So decoding circuit determines the desired unit and connects it to bus. Other devices are effectively disconnected so that they wouldn’t have any affect to bus operations. They are carried out bytri-state buffers.

Tristate buffers allow to isolate circuits from data bus. This means that circuit is switched to high impedance state. Usually we know dual state circuits that can have two logical levels a€?0a€? and a€?1a€?. But there is also widely used tristate logic, where is ability to switch I/O to high impedance state.

Tristate logic can simply be made by two transistors:

tristate.PNG

 

Using such circuit we can have following output results according to input variations:

 

Q1 Q2 Output

OFF OFF High Impedance

OFF ON 0V

ON OFF 5V

 

Simply speaking when output pin is in high impedance state it is physically disconnected from circuit.

 


Reprinted Url Of This Article:
http://www.scienceprog.com/how-does-tri-state-buffers-work/