Implementing a FSM using JK flip flops in VHDL

Question

This is yet another semester project I'm stuck on. I need to implement a state machine starting from the following diagram:

What I've managed to do so far is write this state table, although I'm pretty sure I've gotten something wrong even up to here.

I believe the next step would be drawing a Karnaugh map, but I have no idea how to assign the input values.

It also says I need to use a 8x4 memory, but I'll worry about that once I get to it. For the moment, I'm stuck on the K-map. Any help? Is the table at least correct?

Answer 1

The state table is over-complicated. If you use appropriate values drawn from the set [0,1,a,b] for each flop's J,K inputs, you can reduce it to only 8 entries. Which may give you some indication how to proceed with the next step.

I'll make one observation on the exercise : specifying the use of J-K flipflops may be OK for teaching - it's important to understand the fundamental building blocks. But once you see how it all fits together, it's simpler and more practical to implement the SM behaviourally, something like:

library ieee;
use ieee.std_logic_1164.all;

entity State_Machine is
   port ( Clock : in std_logic );        
end entity;

architecture Behavioural of State_Machine is

-- State could be an integer
--   type State_Type is range 0 to 7;
-- or an enumeration
   type State_Type is (s0, s1, s2, s3, s4, s5, s6, s7);
   signal State : State_Type;
   signal a,b : boolean;

begin

SM: process(clock) is

   function switch (test : Boolean; T,F : State_Type) return State_Type is
   begin
      if Test then
         return T;
      else
         return F;
      end if;
   end switch;

begin
   if rising_edge(clock) then
      case State is
      when s0 => State <= switch(a, T => s1, F => s7);
      when s1 => State <= switch(b, T => s2, F => s6);
      when s4 => State <= switch(b, T => s5, F => s3);
      when s5 => State <= switch(a, T => s6, F => s2);
      when s7 =>
         if a then 
            State <= s0; 
         end if;
      when others => State <= State_Type'succ(State);
      end case;
   end if;
end process SM;

end architecture;