Moore Circuit from text

  • Thread starter DenDanne
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  • #1
DenDanne
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Summary:: I have a problem getting the circuit of the problem to a Moore-solution.

"Construct a Moore Machine and show it in a circuit, that outputs '1' whenever the sequence '01' is encountered in any input binary string (using D-flipflops)".

First of, I have written the Moore Machine.
Untitled.png


I don't think this is where the problem is, as it is quite straight forward in that step.

From this Moore Machine, I do a truth table.
Capture.PNG


And then I use Karnough-diagrams to find equations for A+, B+ and U.
Capture2.PNG

Here is where I get some troubles.
Because by definition of Moore machines. The output shall only be a result of the present state and some output combinatorial logic. NOT the the input. (that is mealy). But as you can see, I get an I in the output formula. So using this method I get an output dependent on the input, which is not allowed!

What have I thought wrong about?
 

Answers and Replies

  • #2
berkeman
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Welcome to PF. :smile:

The next state does depend on the input and the current state, as you have shown. The output only depends on the state, so get rid of the I term in that equation -- it is not used.
 
  • #3
DenDanne
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berkeman said:
Welcome to PF. :smile:

The next state does depend on the input and the current state, as you have shown. The output only depends on the state, so get rid of the I term in that equation -- it is not used.
Thanks!
But if I Karnough without input I, then I get U=A'B. And the problem with this is that there are two times when 01 is the state. Or should I use Karnough on A+ and B+ (next states), that would solve the problem since A+ is only 1 once. But I have never used Karnough on "next states" before.
 
  • #4
berkeman
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When you are in state 01, the output is 1, and it is 0 otherwise. You have 2 FFs in the circuit, so the combinatorial circuit to generate the output takes the outputs of the two FFs as inputs.

If they are DFFs, the input D terms come from the two K-maps that you have above for the next state.
 
  • #5
DenDanne
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berkeman said:
When you are in state 01, the output is 1, and it is 0 otherwise. You have 2 FFs in the circuit, so the combinatorial circuit to generate the output takes the outputs of the two FFs as inputs.

If they are DFFs, the input D terms come from the two K-maps that you have above for the next state.
But according the the State Diagram. The output is 0 when I am in state 01? Only in 10 is the output 1. Hence, I'm thinking that U=AB' is correct for U?
 

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