What is high impedance state in three-state buffer? Explain three state gate in designing bus system.

 A bus can be constructed in two ways

1. Using Multiplexer
2. Using three state buffer

Three state buffer is a useful device that allows us to control, when current passes through a device and when it does not.

Bus system construction using tri-state buffer

1. As in a conventional gate, 1 and 0 are two states.
2. The third state is a high impedance state.
3. The third state behaves like an open circuit.
4. If the output is not connected, then there is no logical significance.
5. It may perform any type of conventional logic operations such as AND, OR, NAND, etc

Active “LOW” Tri-state Buffer

Symbol	Truth Table
Tri-state Buffer	Enable/Control	IN	OUT
	0	0	0
	0	1	1
	1	0	Hi-Z
	1	1	Hi-Z
Read as Output = Input if Enable/Control is NOT equal to “1”

 

Active “HIGH” Tri-state Buffer

Symbol	Truth Table
Tri-state Buffer	Enable/Control	IN	OUT
	0	0	Hi-Z
	0	1	Hi-Z
	1	0	0
	1	1	1
Read as Output = Input if Enable/Control is equal to “1”

 

Three-state buffer gate

1. To form a single bus line, all the outputs of the 4 buffers are connected together.
2. The control input will now decide which of the 4 normal inputs will communicate with the bus line.
3. The decoder is used to ensure that only one control input is active at a time.
4. The diagram of a 3-state buffer can be seen below.

 

Figure – Bus Line with three-state -buffers

 

 

 

Some Other Question :

• Explain the Common Bus System with its diagram.
• Explain the register transfer language with example.
• What is high impedance state in three-state buffer? Explain three state gate in designing bus system.
• Explain 4-bit Arithmetic Circuit with its Function Table
• Discuss the phases of Instruction Cycle with flowchart.
• Explain the basic working principle of the Control Unit of basic computer using diagram.