Larger Decoders (4/6) 1 0 disabled 1 1 enabled 3x8 Dec S2 w x y 1 : 7 F0 w'x'y' F1 w'x'y F7 wxy 2x4 Dec S1 S0 1 2 3 F0 w'x'y' F1 w'x'y F2 w'xy' F3 w'xy E F4 wx'y' F5 wx'y.
65 Using Smaller Multiplexers (2/6) Lets enable look at this example: F(A,B,C) S m(0,1,3,6) ABC ABC ABC ABC AB mux F mux A B 1 2 3 C C' F Note: Two of the variables, A, B, are applied as selection lines of the multiplexer, while.Decoders: decoder Implementing Functions (1/5 enable a Boolean function, in sum-of-minterms form a decoder to decoder generate the minterms, and an OR gate to form the sum.D4, d5, d6, d7 x x x When the Enable pin (E) is low all the output pins are low.(b) Implementation with 74151A.Useful MSI circuits Decoders Implementing Functions with Decoders Decoders with Enable Larger Decoders Standard MSI Decoders Implementing Functions with Decoders (2) Reducing Decoders 3, enable lecture 7 Combinational Circuits: MSI Components.Example: F(A,B,C) A'B'C A'BC AB'C ABC' S m(1,3,5,6) (ii) Connect n variables to the n selection lines.1 to 8 demux Circuit Diagram 1 to 8 Demux circuit 3 to 8 Decoder/Demultiplexer IC 74HC238 is used is used as decoder/ demultiplexer.The decoder decoder circuit works only when decoder the Enable pin (E) is high.The circuit is designed with AND and nand logic gates.51 Multiplexer (5/5) An application: Helps share a single communication line among a number of devices.Implemented with OR gates.Applications of Demultiplexer Used to connect a single source with to multiple destinations. 44 Encoder (5/5) Example: Octal-to-binary encoder.
32 Reducing Decoders codec (6/13) So we can save a decoder.
However, with we can use a single smaller 2(n-1)-to-1 multiplexer to implement any Boolean function of n (input) variables.
An 8-to-3 encoder z plus D1 D3 D5 D7 y D2 D3 D6 D7 x D4 D5 D6 D7 An 8-to-3 encoder Exercise: Can you design a 2n-to-n encoder without the K-map?57 Larger cook Multiplexers (5/6) Another implementation of an 8-to-1 multiplexer using smaller multiplexers: When S2S1S0 000 4:1 MUX S2 S1 I0 I1 2:1 MUX S0 I2 decoder I3 I4 I5 I6 I7 I0 I4 I2 I6 I0 Y Q: Can we use only 2:1 multiplexers?The below is the truth table for 1 to 2 demultiplexer with I as input data, D0 and D1 are the output data line and A is the selection line.This may be eliminated.Din is the input data, S0, S1, full and S2 are select inputs and Y0, Y1, Y2, Y3, Y4, Y5, game Y6, Y7 are the outputs.Of) 2n output lines.58 Larger Multiplexers (6/6) A 16-to-1 multiplexer can be constructed from five 4-to-1 multiplexers: 59 Standard MSI Multiplexer (1/2) 74151A 8-to-1 multiplexer.27 Reducing Decoders (1/13) Example: F(a,b,c) m(4,6,7) Using a 38 decoder (assuming 1-enable and active-high outputs).11, decoders: Implementing Functions (2/5 example: Full adder S(x, y, z) S m(1,2,4,7) C(x, y, z) S m(3,5,6,7) 3x8 Dec S2 S1 S0 x y z S.3 to 8 line decoder circuit is also called as binary to an octal decoder.We take the first and fourth outputs from each decoder).