### EE 231 Lab 2: Basic Combinational Circuits using SSI IC's

This lab requires the analysis, design, and construction of two combinational circuits. Doing the prelab before coming to lab will get you out on time. Waiting until your lab session WILL KEEP YOU IN THE LAB WELL PAST DINNER.

#### Part 1. A Simple Circuit.

Recalling the circuit shown in Figure 1 of your prelab, answer the following questions:

• Is it better to test the circuit as you go along in the building process, or should you  wait until the end and test everything at once?
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• What instrument will you use to do this testing?
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• How will you verify that the truth table for the completed circuit is the same as the original truth table?
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• How did you convert a 3-input NAND gate into a 2-input NAND gate?
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Wire the circuit and make sure it works. Have your lab instructor verify that your circuit works.

#### Part 2: Logic Analyzer

In this portion of the lab you will use a digital logic analyzer and stimulus generator to verify that your circuit, constructed in Part 1, works as required.

1. The stimulus generator consists of a counter whose outputs are the input signals (A, B, and C) to the circuit under test. For this lab you are going to use a 12-stage Binary Ripple Counter, the 74HC4040A. The output of each flip-flop feeds the next, and the frequency at each output is half of that of the preceding one. The state counter advances on the negative-going edge of the clocking input. The reset (pin 11) is asynchronous and active-high. Use Q1 (pin 9) as input A, Q2 (pin 7) as input B, and Q3 (pin 6) as input C. Connect Q4 (pin 5) to the Reset input (pin 11) of the same counter.
2. To make sure the counter supplies the sequence needed (000, 001, ... , 111), use a low frequency clock signal (select a TTL square wave) from the protoboard clock as the clock input (pin 10) signal to the counter; connect the Q1-Q3 outputs of the counter to the LEDs of the protoboard. The LEDs should display the desired sequence.
3. Now, let's make the connections to the logic analyzer. Start up the logic analyzer, like you did in last week's lab. Connect inputs for the analyzer to A, B, C and  the output (Y) of your circuit. Capture a waveform, and verify that it is correct.

Don't be shy about getting the lab assistants if you have difficulty in setting up the stimulus generator or the logic analyzer.

#### Part 3. The Majority Circuit.

In this section of the lab you will build and test the majority circuit which you designed in the Part 3 of your prelab.

After your circuit is competed, use the stimulus generator (described in Part 2) and logic analyzer to verify that the circuit works.

August 2000