Help JK FlipFlop

[Cedric Jan Montemayor]

Hello guys, we really need help constructing a circuit about JK Flipflop with the use of 555 timer as the clock. There are 3 leds as the output and they must turn of/off synchronously using the truth table. here is the output

C B A
0 1 0
1 0 1
0 1 1
1 1 0

PLS HELP

 

[Harald Kapp]

This is an assignment, right? I therefore put it into the homework forum.

1. Start by assigning one JK-FF to each output A, B and C. Assume that upon reset all flipflops are set to Q=0, \Q=1 (typically you will have to provide a separate reset signal for this to happen).
2. Define which of the states in your truth table is the initial state after reset. Chose Q or \Q from teh flipflops as outputs A, B and C such that these outputs represent the initial state after reset.
3. find the logic equations (boolean equations) that define the next output state (A(t+1), B(t+1), C(t+1)) in terms of the current state (A(t), B(t), C(t)) and using this find the equations how to set up the J and K control inputs such that the JK-FF will change to the desired state with the next clock.

Here are some examples how the flipflop's outputs plus some logic can be used to create diffferent behavior. Show us your effort for a sanity check.

 

[Cedric Jan Montemayor]

help I can't get the output

 

[Harald Kapp]

This circuit can't do what it is required to do. The leftmost output is equal to the clock and therefore changes twice within each clock cycle. A state machine as (although very briefly) described in your 1st post changes with every active clock edge (typically one choses the rising edge top be active). You will need a 3rd flipflop for the leftmost output.

A few more issues:

1. label the outputs, so one can see which one is supposed to be A, b OR c.
2. Make the circuit a synchronous one (currently it is asynchronous, this will not be suitable for this task).
3. J and K will not be simply tied to the same signal (the box labeled '1' in your diagram). You will need some logic (gates) to perform the necessary boolean equations to set up J and K for each flipflop such that upon the next active clock edge the output changes to the required state (0/1) as defined by your truth table. Se the 'examples' link in my 1st answer.