Digital Circuits/Encoders-Decoders

Encoders and decoders are similar to multiplexers and demultiplexers, except that they are a little bit more complicated.

Decoders

Decoders will have N inputs, and $2^{N}$ output. Let's say that we have two inputs (A and B), and 4 outputs (M N O P). Decoders will satisfy the following truth table:

A	B	M	N	O	P
0	0	1	0	0	0
0	1	0	1	0	0
1	0	0	0	1	0
1	1	0	0	0	1

Binary numbers come in, and essentially select which wire to send a signal on. chankana

Encoders

Encoders work in exactly the opposite way as decoders, taking $2^{N}$ inputs, and having N outputs. When a bit comes in on an input wire, the encoder outputs the physical address of that wire.It takes 2^n inputs and gives out n outputs,the enable pin should be kept 1 for enabling the circuit.

Truth Table for 4:2 encoder circuit

Y3	Y2	Y1	Y0	A	B
0	0	0	1	0	0
0	0	1	0	0	1
0	1	0	0	1	0
1	0	0	0	1	1

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Priority Encoders

A Priority Encoder works opposite of the decoder circuit. Priority Encoders have logical ranking within them, input₁ may be higher than input₂. If input₂ and input₁ were pressed, the encoder would determine the priority, and accept the input.

Encoders and Multiplexers

The relationship between the two.

A multiplexer (MUX) is a combination circuit that contains more than one input line, one output line and more than one selection line. Whereas, an encoder is also considered a type of multiplexer but without a single output line.It is a combinational logic function that has 2^n (or fewer) input lines and n output lines.

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