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Stumped on a state machine design

  1. Jun 14, 2008 #1
    1. The problem statement, all variables and given/known data

    Design a state machine that repeatedly goes through the following sequence: three repeats of 0,2,4,6 followed by 2 repeats of 1,3,5,7. An observer watching the machine should see the states over and over: 0,2,4,6,0,2,4,6,0,2,4,6,1,3,5,7,1,3,5,7...


    3. The attempt at a solution


    I've decided to use a 4 bit counter as the input to the machine. I have set up the following truth tables:


    EDIT: it is chewing my formatting to pieces. The values on a line by themselves are the counter values.


    Counter current state next state

    00
    000 010
    001 011
    010 100
    011 101
    100 110
    101 111
    110 000
    111 000
    01
    000 010
    001
    010 100
    011
    100 110
    101
    110 000
    111
    10
    000 010
    001
    010 100
    011
    100 110
    101
    110 001
    111
    11
    000
    001 011
    010
    011 101
    100
    101 111
    110
    111 001



    I seem to run into a problem after the first complete 3-2 sequence.(Thus why the truth table isn't completed.) When the counter is at 00, 01, and 10, the sequence is at 0246. It then swaps to the 1357 sequence at counter values 11 and 00. After that, instead of counting three more 0246 sequences, it swaps back to 1357 at the end of counter value 10. This problem would be simple if the sequences alternated every 4 times but, my machine seems to overlap itself when the counter runs back through the values. Any ideas how to correct the problem?
     
  2. jcsd
  3. Jun 14, 2008 #2
    I may have found an alternate way to solve this. Does anyone know if there is a way to make a 3 bit counter stop at 5 and start back over at 1?
     
  4. Jun 14, 2008 #3
    Do you have to use a counter? It seems this would be a very easy problem with a simple microprocessor.
     
  5. Jun 15, 2008 #4
    Didn't see the reply in time but I solved it anyway. I decided to use a second state machine for the input that rotated through 5 states of 0,0,0,1,1


    Thanks for the help.


    JH
     
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