# 3 Bit Counter J-K FF's

Discussion in 'Homework Help' started by djplayer, Dec 2, 2008.

1. ### djplayer Thread Starter New Member

Nov 12, 2008
2
0
decently timely assignment.. at least IMO.

Design a Bit Synchronous counter that counts 0,2,4,7,0 etc.. when input x=0, and counts 1,2,5,7,1 etc.. when x =1. Use JK FF's to Design the circuit using the listed methods:

1. SOP
2. NAND only
3. POS
4. NOR only
5. Minimal # of 1 of 4 mux's plus NOT gates if needed
6. Minimal # of 3 to 8 line Decoders plus NAND Gates

essentially I'm just trying to get started right now.. To be honest a decent amount of this is NOT covered in class. Alot is not in the book.

I found these steps for creation of Synchronous counters:
-Identify the states and number of states.
- Calculate # of FF's required. FF = 2^n states.. so I'd be 8
- I would use the excitation table for JK
- Construct Truth Table w/ Present, next, excitation inputs for FF
- Construct K map w/ present state as input and excitation input as ouput
- Solve K-MAP and obtain the expression for excitation stable input
- repeat last 2 steps for all inputs

which sounds all great.. but I haven't even touched the timing diagram. Or the fact that I have to use: SOP, NAND, NOR etc.. etc..

a little help would be greatly appreciated.

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
You only need 3 flip flops - 0 is 000, 7 is 111. It's a state machine, where the current state plus the X level sets the J & K conditions so the next clock produces the next state.