# how many j k flipflop needed to count the series 0..1..0..2..0..3...0..1..0..2..0..3.. and so on

Discussion in 'Homework Help' started by Debasmita Bhoumik, Feb 14, 2016.

1. ### Debasmita Bhoumik Thread Starter New Member

Feb 14, 2016
2
0
i think it will be 2. cz
q1 q0
0 0
0 1
0 0
1 0
0 0
1 1
0 0

2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
8,785
771
Welcome to AAC
2 outputs, I say 2 FF

3. ### RBR1317 Active Member

Nov 13, 2010
264
54
Consider how many unique states of '00' there are, i.e., when the next state after '00' produces a different result. How will the logic know which '00' state in the sequence it is at if there are only 2 FF?

4. ### MrChips Moderator

Oct 2, 2009
12,623
3,451
RBR is correct.

You are trying to design a state machine. Ask yourself how many unique states there are.

0 1 0 2 0 3 ...

There are six unique states. How many flip-flops will you require for six states?

5. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
A simple AND gates with a ripple counter would do it. The clock has to be a square wave.

2 flip flops, 2 AND gates, and the clock.

Need a schematic?

6. ### Debasmita Bhoumik Thread Starter New Member

Feb 14, 2016
2
0
wendy, can u plz explain a little more?

7. ### RBR1317 Active Member

Nov 13, 2010
264
54
A signal chopper on the Q outputs will certainly display the correct series of numbers, but it will not 'count' the series.

Last edited: Feb 15, 2016
8. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
True enough, so you add a flip flop and do it. I'll try to draw something up.

9. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
OK this is not complete, but it should give you the idea. I suspect this is homework, so it would not hurt for you to complete it.

10. ### RBR1317 Active Member

Nov 13, 2010
264
54
The problem of designing ripple counters, with gated outputs no less, is that it is a hit or miss operation. However, there are established design procedures for creating a fully synchronous sequential state machine using JK flip-flops. I tried to get a LibreOffice spreadsheet to implement the transition mapping procedure, starting with the sequential state table to automatically produce the sequential transition table, the index transition table, and from that to automatically draw the Karnaugh transition maps. However, it is still a manual process to go from the sequential table to the index table. Also, the spreadsheet has problems with persistent formatting of Boolean results to display as simple numbers (TRUE, FALSE vs 0,1). Nevertheless, here is the result of one possible design of a state machine to count 0,1,0,2,0,3,0,1... using 4 JK FF.