CSC270    Lab #5

EXPERIMENT 1: Multiplexer

The questions and instructions throughout these experiments are guidelines to get you started. You need to think about what you are doing, what other questions might be interesting and appropriate, and also decide for yourselves what you need to test and report upon in order to fully investigate and describe each circuit. Note: the logic switches may be useful in this and other experiments.

Implement the following function f of three variables, I0, I1, and Cmd:

        f = I0.Cmd' + I1.Cmd

Connect Cmd to one of the data switches, I0 to the 1Hz clock, and I1 to another data switch. Connect f to a logic indicator.

Label each signal on your kit with a post-it or piece of paper.

What is the truth table for f?

What is the simplified truth table for f?

You have implemented a multiplexer. Explain why it "multiplexes", and how you observe the multiplexing behavior.

EXPERIMENT 2: A First Latch

In the next series of experiments you will be building at each step on what you have just done. So - it might be useful to read through the entire lab now and plan out where to place each chip and how to wire the circuits.

Implement the circuit below, and investigate its behavior, developing a full description of this circuit:

1. Whether it behaves in predictable ways,
2. What properties it has,
3. What is good and bad about this circuit?,
4. etc.

EXPERIMENT 3: A Latch with a Control input

Now implement the next circuit below to make a D latch with a control input and fully investigate the behavior of this circuit, reporting what you did, expectations, observations, results and things you learned, etc.

EXPERIMENT 4: A Clocked Flip-Flop

To complete your flip flop, connect two of the D latches with control together, as seen in class, to make a master-slave flip flop.


What does it mean for a flip-flop to be triggered by the positive versus the negative edge of the clock? Does this flip flop have positive or negative edge response? How would you change this circuit to respond to the other edge?

To investigate and test your circuit

1. Connect both the Clock and Q signal to logic indicators.

2. Build your circuit in stages and test each stage alone before proceeding to the next stage. Connect stages together only when you are certain each stage works as anticipated on its own.

3. Test your circuit with data switches on the two inputs (D and CLK), to test that each input combination results in the expected state / output (i.e., you will operate one switch to act as a very slow clock, so that you have time to observe everything of interest the first time through). Does the circuit behave as expected? Why or why not?

4. Once you are certain each stage works correctly, connect them all together, and connect the clock input to the Clock signal of the kit. Set this signal to 1 Hz (1 cycle per second). Also connect the Q-bar output to the D input.

   Does this circuit work as expected? Why or why not?

   What is the frequency at which the Q output oscillates? What is the relationship between the frequency of Q and the frequency of the clock input (hints: half or double?) Does your flip flop wired this way behave as a frequency multiplier or a frequency divider?

Record what you have done, including a complete wiring diagram, along with intermediate results (including relevant internal states of the flip flop), expectations and unexpected obsevations, results, etc.