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Unformatted text preview: Mult 1 Multiplexers Today, well 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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 Spring '08
 

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