Review: the decoder circuit
 

Review: A decoder circuit has N control signals and 2N output signals:

The (one) output which is equal to 1 will be used to activate a circuit (usually a memory circuit)

A related circuit: the demultiplexor circuit
 

A demultiplexor circuit has N+1 input signals and 2N output signals:

The data input i is switched to exactly one of the outputs - while all other outputs are equal to 0

Review: operation of a 2x4 decoder
 

Functionality of the 2x4 decoder:

The operation of a 1x4 demultiplexor
 

Functionality of the 1x4 demultiplexor:

Review: How to construct a 2x4 decoder using (basic) gates
 

Internals of a (2x4) decoder:

DEMO: /home/cs355001/demo/circuits/decoder

Review: How to construct a 1x4 demultiplexor using (basic) gates
 

Internals of a (1x4) demultiplexor:

DEMO: /home/cs355001/demo/circuits/demux

Usage of demultiplexors
 

  • The demultiplexor circuit is not used (much) inside a computer

  • Demultiplexor is used in communication systems

    In this scenario, the demultiplexor is often used in conjunction with the multiplixor to create a inexpensive (cheap) switching network

Example of using demultiplexor
 

This simple (one-way) digital switch can switch one signal from any input port onto any output port (= a small (digital) telephone switch):

DEMO: /home/cs355001/demo/circuits/mux-demux