Objective:
In this experiment, you will use Logisim to analyse and design sequential circuits.
Part I
1. Run Logisim, open the file lab10part1.circ. The circuit is shown below.
The circuit consists of two JK flip-flop and an OR gate. Note the following:
The outputs of the two JK flip-flops are labelled A and B, which form the state of the circuit.
The Clock is connected to the clock inputs of the flip-flops.
The logic constant 1 is connected to the Enable inputs of the flip-flops.
The Clear switch is connected to the clear inputs of the flip-flops. Hence when Clear = 1, it clears the contents of both flip-flips to 0, bringing the circuit to the initial state of AB=00.
The flip-flop inputs are as follows:
AY2019/20 Semester 2 - 1 of 3 - CS2100 Lab #10
For flip-flop A:
JA=A+B;
KA=0
For flip-flop B:
JB=1;
KB=A+B
3. Complete the following table:
[6 marks]
Present state
Flip-flop inputs
Next state
A
B
JA
KA
JB
KB
A+
B+
0
0
0
1
1
0
1
1
Verify the correctness of your table above by testing the circuit in Logisim.
Click on “Clear” input to get 1. This clears both flip-flops to 0, bringing the circuit to the initial state of AB=00.
Click on “Clear” input to get 0 before you proceed. This puts the flip-flops in their normal operation mode.
Clicking the “Clock” input toggles its value. When the “Clock” value changes from 0 to 1 (i.e. a rising edge), the flip-flops react according to the commands at their J and K inputs.
Click the “Clock” input several times to simulate the square wave, and watch the outputs of the flip-flops change their values. Do the values follow your table above?
If at any point of time you want to reset the flip-flops to the initial state of 00, go to step (a) above.
5. Complete the state diagram below. [4 marks]
00
01 10
11
AY2019/20 Semester 2 - 2 of 3 - CS2100 Lab #10
Part II
You will design a sequential circuit using JK flip-flops. The flip-flop inputs are given below:
For flip-flop A:
JA=1;
KA=A B
For flip-flop B:
JB=0;
KB = (A B)'
7. Complete the following table:
[6 marks]
Present state
Flip-flop inputs
Next state
A
B
JA
KA
JB
KB
A+
B+
0
0
0
1
1
0
1
1
8. Complete the state diagram below.
[4 marks]
00
01
10
11
9. Implement the circuit on Logisim and save it under lab10part2.circ and send it to your lab TA along with the completed lab report. In your circuit, you should also include a “Preset”
input so that you can set both flip-flops to 1. [5 marks]
10. As this is your final lab, your lab report will not be returned to you.
Total: 25 marks
AY2019/20 Semester 2 - 3 of 3 - CS2100 Lab #10
