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# Multiplexer demul

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### Multiplexer demul

1. 1. Example of a Combinatorial Circuit: A Multiplexer (MUX) <ul><li>Consider an integer ‘m’, which is </li></ul><ul><li>constrained by the following relation: </li></ul><ul><li>m = 2 n , where m and n are both integers. </li></ul><ul><li>m=no of inputs </li></ul><ul><li>n=no of control inputs </li></ul><ul><li>A m-to-1 Multiplexer has </li></ul><ul><ul><ul><li>m Inputs: I 0 , I 1 , I 2 , ................ I (m-1) </li></ul></ul></ul><ul><ul><ul><li>one Output: Y </li></ul></ul></ul><ul><ul><ul><li>n Control inputs: S 0 , S 1 , S 2 , ...... S (n-1) </li></ul></ul></ul><ul><ul><ul><li>One (or more) Enable input(s) </li></ul></ul></ul><ul><li>such that Y may be equal to one of the inputs, depending upon the control inputs. </li></ul>
2. 2. Example: A 4-to-1 Multiplexer <ul><li>A 4-to-1 Multiplexer: </li></ul>I 0 I 1 I 2 I 3 S 0 S 1 Y 1 output n control inputs 2 n inputs Enable (G)
3. 3. Characteristic Table of a Multiplexer <ul><li>If the MUX is enabled, </li></ul><ul><li>s 0 s 1 </li></ul><ul><li> 0 0 Y=I 0 </li></ul><ul><li> 0 1 Y=I 1 </li></ul><ul><li> 1 0 Y=I 2 </li></ul><ul><li> 1 1 Y=I 3 </li></ul>
4. 4. Multiplexer: Example 1 <ul><li>using a 16-to-1 multiplexer: </li></ul>F I 0 0 0 1 0 I 1 I 2 I 3 I 4 I 5 I 8 I 6 I 9 I 7 I 11 I 10 I 13 I 12 I 14 I 15 0 0 0 0 1 1 1 1 1 1 1 1 S 3 S 2 S 1 S 0
5. 5. Multiplexer: Example 2
6. 6. Multiplexer: Example 3 Z X Y
7. 7. Multiplexer: Example 4
8. 8. Demultiplexer (DMUX)/ Decoder <ul><li>When used as a demux their basic function is to take a single line input and send it to one of the several outputs depending upon the value of selection inputs. </li></ul><ul><li>When used as a decoder.Their basic function is to accept a binary word (code) as an input at the selection inputs and create a different binary word as an output . </li></ul>
9. 9. The diagram below shows the relation between a multiplexer and a Demultiplexer . I0 I1 I2 I3 S1 S0 Y out Y0 Y1 Y2 Y4 S1 S0 Input 4 to 1 MUX 1 to 4 DEMUX
10. 10. Characteristic table of the 1-to-4 DMUX : Table 1
11. 11. A Decoder is a Demultiplexer with a change in the name of the inputs : When the IC is used as a Decoder, the input I is called an Enable input Y0 Y1 Y2 Y4 S1 S0 ENABLE INPUT 2 to 4 Decoder
12. 12. Characteristic Table of a 2-to-4 DECODER, with ACTIVE LOW Outputs and with ACTIVE LOW Enable Input: Table 2