CSE370 Quiz 4
(21 May) Solution
Below is a sequential circuit and the skeleton of a state diagram.
Reverse-engineer the circuit to derive the state diagram. Do this
by considering each state individually and looking at what the next state
and output values are for the state given the possible values of the input.
1. Is this a Mealy or Moore machine?
Mealy (output is a function of input and state)
2. Derive the state diagram and draw it in the skeleton below (note: 01
implies Q1 = 0, Q0 = 1). Show all state transitions and outputs.
Begin by writing down the equations for the output (O), D1, and D0 in terms
of the input (I), Q1, and Q0.
O = I' Q0
D0 = Q0 Q1 + I Q1'
D1 = Q0 Q1 + I' Q0
3. Are there any unreachable states? If so, which? You may
assume that 00 is the start state.
11 is unreachable (see state diagram below)
4. Is this a self-starting machine? Why or why not?
No, if the machine starts in 11 it will not be able to leave that
state.
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I
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Q1
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Q0
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D1
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D0
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O
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0
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0
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0
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0
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0
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0
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1
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0
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0
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0
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1
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0
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0
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0
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1
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1
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0
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1
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1
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0
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1
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0
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0
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0
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0
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1
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0
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1
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1
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1
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1
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1
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0
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0
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1
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0
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0
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1
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1
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0
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0
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0
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1
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1
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1
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1
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1
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0
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