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Lecture12

# Lecture12 - Announcements ECE 2300 Introduction to Digital...

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Lecture 12: Spring 2010 1 ECE 2300 Introduction to Digital Logic Design Counters Shift Registers Lecture 12: 2 Announcements Lecture 12: Variation on Combinational Lock Two inputs, X1 and X2 Opens when it sees the sequence X1, X2, X2 New input does not have to occur every clock Reset input (clears D FFs) Mealy machine 3 Lecture 12: 4 FSM Representation 0 1 (Unlock=1) X1 X1,X2 Start X1,X2,X2 1 0 0 0 0 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 1 0 X1 X2 0 0 Reset Lecture 12: State X1 1 X2 Meaning Name 00 01 11 10 Start X1 X1,X2 X1,X2,X2 A B C D A,0 B,0 C,0 A,0 A,0 C,0 D,1 A,0 A,0 A,0 A,0 A,0 B,0 B,0 B,0 B,0 next state current state inputs State+Output Table 5 output Lecture 12: State X1 X2 Meaning Q1 Q2 00 01 11 10 Start X1 X1,X2 X1,X2,X2 0 0 0 1 1 1 1 0 00,0 01,0 11,0 00,0 00,0 11,0 10,1 00,0 00,0 00,0 00,0 00,0 01,0 01,0 01,0 01,0 Transition Table 6 Q1* Q2* Lecture 12: State X1 X2 Meaning Q1 Q2 00 01 11 10 Start X1 X1,X2 X1,X2,X2 0 0 0 1 1 1 1 0 00,0 01,0 11,0 00,0 00,0 11,0 10,1 00,0 00,0 00,0 00,0 00,0 01,0 01,0 01,0 01,0 Excitation and Output Equations 7 Q1* Q2* Q1* = Q2•X1’•X2 + Q1•Q2•X1’ Q2* = X1•X2’ + Q1•Q2•X1’ + Q2•X1’•X2’ Unlock = Q1•Q2•X1’•X2 Lecture 12: One-hot State Assignment Each state value has exactly one 1 • Example: 0001, 0010, 0100, 1000 Disadvantage: n D FFs required for n states Potential advantages

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