Asynchronous down counter help please

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    I need to design a modulo 6* d type asynchronous down counter in which gated outputs reset the bistables after the appropiate count is achieved.
    The drawing shows a three stage counter which i can modify.
    A modulo 6* needs to count down 5,4,3,2,1,0 then resets back to 5,4,3,2,1, 0 etc
    I can get it to start at 5 and count down to zero but it always resets back to 7.
    Please help as its doing my head in
    Thanks
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    Mechynick

    I also have this same question but am struggling to get a count. Do I need to edit simulation settings? My waveforms start at 0 then count down from 7. Also, do I need to alter period settings (currently 2ms) Any help would be appreciated.

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    leave circuit as is, connect not Q (QN) outputs to a 3 input nand gate whose output will be 0 when all QN outputs are 1 (count 7) is used to SET flip flop U2 back to 1) (set input shown as triggered on negative edge 1 to 0, so u2 Q =1,QN goes to 0, giving count at QN outputs 101 =5, count now repeats endlessly modulo 6 (5,4,3,2,1,0 repeat). Down count taken from QN outputs count out
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    Hi Eric what do you mean by "Set input shown as triggered on negative edge 1 to 0" I have the same question and can't get the curcuit working unless I put a Not gate on U2 and connect two of the Nand gate inputs to the not gate of U2 and the output of U2 which does not make logical sense. Thanks
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    Here are some ideas to get you started, when I worked through it as you can see its hand written and instead of Q1,Q2,Q3i have used Q0, Q1, Q2 hope this helps.
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  2. File Type: pdf asyncdncounter2.pdf (131.7 KB, 24 views)
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    (Original post by eric reed)
    Here are some ideas to get you started, when I worked through it as you can see its hand written and instead of Q1,Q2,Q3i have used Q0, Q1, Q2 hope this helps.
    Really helpful Thanks
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    Did you get this to work....I can get it to count from 6 to 1 but not 5 to 0
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    Hi eric, if you get a second, would you be able to post a copy of your final p spice circuit drawing, I appreciate your time, thanks in advance.
 
 
 
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