Lecture 39

Lecture 39 - ECE52 Spring 11 Lecture 39 4/20/11 1...

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1 ECE52 Spring 11 Lecture 39 4/20/11
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2 Asynchronous examples Ex 9.19, 9.20 p. 649ff (655 in 3 rd )(linked) Ex. 9.5 p. 595 (601 in 3 rd ) esp state assignment Ex. 9.7 State reduction introduction
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3 Ex. 9.19/20
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4 Ex. 9.19/20 Model delay here: Y 1 y 1 etc
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5 Ex. 9.19/20 Model delay here : Y 1 y 1 etc 2 2 1 1 1 2 2 2 1 1 1 2 2 1 1 y z y w y w w Y y y w y w w w Y = + + = + + =
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6 True unspecified entry Potential unspecified entry but B to C passes through; leaving gives a safe race
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7 Any hazards in this circuit? 2 2 1 1 1 2 2 2 1 1 1 2 2 1 1 y z y w y w w Y y y w y w w w Y = + + = + + =
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8 Yes! Y 1 ok, but Y 2 ?
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9 Yes! Y 1 ok, but Y 2 ? add y 1 y 2 to Y 2 to fix 2 2 1 1 1 2 2 2 1 1 1 2 2 1 1 y z y w y w w Y y y w y w w w Y = + + = + + =
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10 Ex 9.5 Asynch mod-4 counter Key is need for 8 states, not 4, as per analogy with parity circuit need to “eat” the 1’s and 0’s of unknown length Moore design: 1 1 0 A 0 H 0 B 1 G 3 0 0 1 1 C 1 F 3 D 2 E 2 1 0 1 0 0 1 1 0 0
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11 1 1 0 A 0 H 0 B 1 G 3 0 0 1 1 C 1 F 3 D 2 E 2 1 0 1 0 0 1 1 0 0 Present Next state Output state w = 0 w = 1 z A A B 0 B C B 1 C C D 1 D E D 2 E E F 2 F G F 3 G G H 3 H A H 0 (a) Flow table Present Next state state w = 0 w = 1 Output y 3 y 2 y 1 Y 3 Y 2 Y 1 z 2 z 1 000 0 00 001 00 001 011 0 01 01 011 0 11 010 01 010 110 0 10 10 110 1 10 111 10 111 101 1 11 11 101 1 01 100 11 100 000 1 00 00 (b) Excitation table Key is state assignment! Gray Code to the rescue! equations then follow (in book)
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12 State reduction in asynchronous logic Initial flow tables are likely to have many don’t cares (unspecified entries) from the “change only 1 input at a time” constraint. Can we exploit these to reduce states?
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13 Simple vending machine - asynch A 0 B 0 C 1 D 0 E 1 F 1 0 0 0 0 0 0 D N N N N D D 0 D accept nickel, dime; candy costs 10 cents; no change
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This note was uploaded on 07/05/2011 for the course ECE 52 taught by Professor Dr.jonathanboard during the Spring '11 term at Duke.

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Lecture 39 - ECE52 Spring 11 Lecture 39 4/20/11 1...

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