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#1




Designing a 3bit counter with D flip flops
I have officially reached my wits end.
I have been working on this project now for 20 hours and I have absolutely nothing to show for it except some holes in the walls (oops). My problem is thus: Design a 3 bit counter using 3 D flip flops and one X input. When X is 0, the counter is supposed to count up in multiples of 2 (i.e. 000, 010, 100, 110, 000, etc.). When X is 1, the counter is supposed to count down by odd numbers (i.e. 111, 101, 011, 001, 111, etc.). If X is changed while the counter is going up, the circuit should go to the next lowest odd number on the next clock pulse. If X is changed while the counter is going down, the circuit should go to the next highest even number on the next clock pulse. So there it is. I have designed state table after state table and I cannot find the correct logic to implement this counter to save my life. Any help would be greatly appreciated. Thanks. 
#2




Convert your state tables to a truth table ,then make Kmaps for each of your outputs and find the simplest SOP or POS solution.
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#3




You actually have a twobit up/down counter based on X. The LSB is always equal to the last latched value of X.

#4




I must be utterly stupid because I don't understand any of this. And Caveman, I misrepresented the numbering system. It should probably look more like this:
0000  0010  0100  0110  0000 1111  1101  1011  1001  1111 The way in which it is counting is dependent on the X input. To Mik: I have converted my state table to a truth table but maybe I am doing it wrong. Let me see if I can explain how it looks. [html] X Current State Next State DFF1 DFF2 DFF3 0 000 010 0 1 0 0 010 100 1 0 0 0 100 110 1 1 0 0 110 000 0 0 0 1 111 101 1 0 1 1 101 011 0 1 1 1 011 001 0 0 1 1 001 111 1 1 1 0 111 000 0 0 0 0 101 110 1 1 0 0 011 100 1 0 0 0 001 010 0 1 0 1 000 111 1 1 1 1 010 001 0 0 1 1 100 011 0 1 1 1 110 101 1 0 1 [/html]Is that correct so far? 
#5




WOOOOOOOOHOOOOOOOOOOO!!!!!!
I finally got it!! Thank you so much for the replies. It definitely kicked my mind into overdrive and something just clicked. 
Tags 
3bit, counter, designing, flip, flops 
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