Transcript Combinational Circuits

Logic circuits for digital systems may be
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Combinational Circuits
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Sequential Circuits
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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
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Combinational circuit with a number of
output lines, only one of which is asserted at
any time, dependent on the pattern of input
lines.
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n inputs and 2n outputs.
1
2
3
21 = 2
22 = 4
23 = 8
Converts binary information from the n coded
inputs to a maximum of 2n unique outputs.
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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 A2=0, upper is enabled; if A2=1, lower is enabled.
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Combinational logic circuit which performs
reverse of decoder functions.
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Accepts an active level on one of its inputs
and converts to a coded output.
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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.