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Unformatted text preview: Mult 1 Multiplexers • Today, we’ll study multiplexers, which are just as commonly used as the decoders we presented last time. Again, – These serve as examples for circuit analysis and modular design. – Multiplexers can implement arbitrary functions. – We will actually put these circuits to good use in later weeks, as building blocks for more complex designs. Multiplexers 2 Multiplexers • A 2 nto1 multiplexer sends one of 2 n input lines to a single output line. – A multiplexer has two sets of inputs : • 2 n data input lines • n select lines, to pick one of the 2 n data inputs – The mux output is a single bit, which is one of the 2 n data inputs. • The simplest example is a 2to1 mux: • The select bit S controls which of the data bits D0D1 is chosen: – If S=0, then D0 is the output (Q=D0). – If S=1, then D1 is the output (Q=D1). Q = S’ D0 + S D1 Multiplexers 3 More truth table abbreviations • Here is a full truth table for this 2to1 mux, based on the equation: • Here is another kind of abbreviated truth table. – Input variables appear in the output column. – This table implies that when S=0, the output Q=D0, and when S=1 the output Q=D1. – This is a pretty close match to the equation. Q = S’ D0 + S D1 Multiplexers 4 A 4to1 multiplexer • Here is a block diagram and abbreviated truth table for a 4to1 mux....
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This note was uploaded on 10/19/2011 for the course CS 231 taught by Professor  during the Spring '08 term at University of Illinois at Urbana–Champaign.
 Spring '08
 

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