 Combinational Circuits
 Sequential Circuits

 Consists of logic gates whose outputs at any time are determined by combining the values of the applied inputs using logical operations.

n inputs
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Combinational
Circuit
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m outputs

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Decoders
Encoders
Counters
Half Adder
Full Adder

 Combinational circuit with a number of output lines, only one of which is asserted at any time , dependent on the pattern of input lines.

 n inputs and 2 n outputs.
 1 2 1 = 2
 2 2 2 = 4
 3 2 3 = 8
Converts binary information from the n coded inputs to a maximum of 2 n unique outputs.

 Larger decoders from small decoders with enable inputs.
 3-8 line decoder from 2-4 line decoders
 6-64 line decoder from 4-16 line decoders

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3-to-8-line decoder constructed from two 2to-4-line decoders
The MSB is connected to the enable inputs if A
2
=0, upper is enabled; if A
2
=1, lower is enabled.

 Combinational logic circuit which performs reverse of decoder functions.
 Accepts an active level on one of its inputs and converts to a coded output.
 The process of converting familiar symbols or numbers to a coded format is called encoding.

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Priority Function.
Highest priority takes precedence.