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The circuit shown in figure is using one 4-bit BCD counter and one 4-bit binary counter. The MOD value for the counter is ?

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I think the answer is 80.

BCD counter counts from 0-9 and starts again (mod 10).

Binary counter counts from 0-15 and starts again (mod 16)

Lets assume initially Binary counter at value 0000.

BCD counter can count on clock pulses, Binary counter increments only when Q3 becomes 1 (ie 8 and 9)

See the figure , I am including, we have 8 cycles of 10 different values . Therefore answer is 80.

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Answer given is 160. I also believe that the binary counter will get incremented only when Q3 is 1 i.e. either BCD counter must have 1000 or 1001 value for the working of binary counter.  As a result answer should be 80.
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If the binary counter is +ve edge triggered , only 1 value of the binary counter is incremented each cycle (at 8 only).Then we have 16 cycles of 10 different values.Then the answer is 160
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Okay got it. Thanks for clarification.