Lab #10: Using Logisim II
[ This document is available on Canvas and course website https://www.comp.nus.edu.sg/~cs2100 ]
Objective:
In this experiment, you will use logisim to analyse and design sequential circuits. Complete Part I before coming to your lab!
Part I
1. Run logisim, open the file lab10.circ. The circuit is shown below.
2. 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:
For flip-flop A: JA = A + B; KA = 0
For flip-flop B: JB = 1;
KB = A + B
Present state Flip-flop inputs Next state
A B JA KA JB KB A+ B+
0 0
0 1
1 0
1 1
4. Verify the correctness of your table above by testing the circuit in Logisim.
a) Click on “Clear” input to get 1. This clears both flip-flops to 0, bringing the circuit to the initial state of AB=00.
b) Click on “Clear” input to get 0 before you proceed. This puts the flip-flops in their normal operation mode.
c) 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.
d) 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?
e) If at any point of time you want to reset the flip-flops to the initial state of 00, go to step (a) above.
Part II
6. During the lab session, you will design a sequential circuit. Your labTA will provide you with the flip-flop inputs. Copy down the flip-flop inputs below:
For flip-flop A: JA = ____________; KA = ____________
For flip-flop B: JB = ____________; KB = ____________
Present state Flip-flop inputs Next state
A B JA KA JB KB A+ B+
0 0
0 1
1 0
1 1
9. You do not need to implement this circuit.
10. As this is your final lab, your lab report will not be returned to you.
