Combinational Circuits

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Logic circuits for digital systems may be

 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.

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Combinational Circuit .

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outputs

     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

   3-to-8-line decoder constructed from two 2 to-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.

  Priority Function.

Highest priority takes precedence.

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