Spring 2002 CSCI 255 Lab 3

This lab is scheduled for 13 & 14, February.

First things first

If you still haven't finished Lab 1 on account of power failure during last week's lab, do it now.

Goals and Methods

This week we'll use the MultiMedia Logic simulator to experiment with clocks, counters, multiplexors, and seven segment displays.

You'll probably want to do this lab with a partner.

Downloading lab files

Four MultiMedia Logic design files, PartA.lgi, PartB.lgi, PartC.lgi, and StopLight.lgi, and one initialization file, SLRAM.txt, are needed for this lab. You can download these as either a Windows self-extracting exe file or a Zip file.

Download and continue.

Part A

Using MultiMedia Logic, open PartA.lgi.
Lab 3 Part A

This circuit contains a seven segment display and a few switches. Your job is to set the switches until the seven segment display shows "2.".

You can wait until after you have completed Part C to get an instructor checkoff.

Part B

Now open PartB.lgi.
Lab 2 Part B

This time we have a seven segment display connected to a counter, our first logic device that remembers its past. Right-click on the counter and select Help to read about its controls. Now figure out how to get the seven segment display to show "5".

Part C

Open PartC.lgi.
Lab 3 Part C

Now we have a clock connected to our seven segment display. Start running the circuit. Notice that it is just too fast. Right-click on the clock and then slow it down so that you can really read the numbers being displayed. You will need to experiment a little.

Instructor check-off

Have your lab instructor look at parts A, B, and C.

Stoplight revisited

Finally, open and run StopLight.lgi.
StopLight circuit
You'll probably need to adjust the clock to get a decent stoplight.

In this design we are ignoring the most significant bit of the counter and have effectively turned a four-bit counter into a three-bit counter. The three-bit count is being sent into a RAM that contains the three bits needed for the LED's. Within the three-bit count; the light is green for counts zero to two, yellow for count three, and red for counts four to seven. Don't worry about how the RAM is initialized to do this. Accept it as magic.

Your job is to reimplement the RAM with combinational logic, either (1) a decoder and a couple of NAND gates; (2), a multiplexor; or (3), "random" logic. The effect of your RAM replacement should be to compute the following truth table.


By the way, here's a picture of a circuit that computes the carry-out function of a full adder in the three ways enumerated above.
Three ways to compute the carry

Instructor checkoff

When you are done, show the lab instructor your work.