Multiplexer, Demultiplexer, Encoder and Decoder

 

1. Multiplexer (MUX)

• Function: Selects one input from many and sends it to a single output.
• Inputs: Multiple data inputs + select lines
• Output: Single output
• Key Idea: Many → One
• Example: 4-to-1 MUX
• 4 inputs: I0, I1, I2, I3
• 2 select lines: S0, S1
• 1 output: Y

2. Demultiplexer (DEMUX)

• Function: Takes a single input and routes it to one of many outputs based on select lines.
• Inputs: Single input + select lines
• Outputs: Multiple outputs
• Key Idea: One → Many
• Example: 1-to-4 DEMUX
• Input: D
• Select lines: S0, S1
• Outputs: Y0, Y1, Y2, Y3

3. Encoder

• Function: Converts 2ⁿ input lines into an n-bit code (binary). Only one input should be active at a time.
• Inputs: Multiple inputs (like 8)
• Outputs: Fewer outputs (like 3 for 8→3 encoder)
• Key Idea: One-hot input → Binary output
• Example: 8-to-3 Encoder

4. Decoder

• Function: Converts n-bit binary input into 2ⁿ outputs. Each input combination activates one output.
• Inputs: Binary inputs (like 3)
• Outputs: Multiple outputs (like 8 for 3→8 decoder)
• Key Idea: Binary input → One-hot output

Quick Comparison Table

Device	Function	Inputs	Outputs	Key Idea
Multiplexer	Selects one input	Many + select lines	One	Many → One
Demultiplexer	Routes input to one output	One + select lines	Many	One → Many
Encoder	Converts 1-hot to binary	Many (1 active)	Few (binary code)	Many → Fewer
Decoder	Converts binary to 1-hot	Few (binary code)	Many	Few → Many