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# Introduction to Computer-Aided Design

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```									ECEN 1521L                      Basic Digital and Computer Circuits Laboratory

Experiment 6                                             NAME
Introduction to Computer-Aided Design
PARTNER

Objectives: To learn the basics of LogicAid and SimuAid, the computer-aided logic circuit
analysis and design programs supplied with the Roth lecture textbook.

1. Analysis and simulation software
Locate the Roth directory on the computer you are using and look at the LogicAid and SimuAid
sub-directories. Depending on the PC installation of Roth software, the directory structure may
differ somewhat. Nevertheless, find and look briefly at both user guides. Also locate the shortcut
to each program on the desktop.
The LogicAid program will be used to simplify logic functions that are entered in different forms
such as minterm or maxterm lists, equation forms, or in truth table forms. SimuAid will be used to
build and test logic circuits on a virtual breadboard.

2. Simplification using LogicAid
(a) Start LogicAid and use the menu help command to learn how to input the description of a
logic function in each of the three basic forms: list form, equation form, or truth table form.
(b) Use what you learn to input a two-input XOR-function in truth-table form. Use A and B as
input variable names and F1 as the output variable name. Also use straight binary order for
input combinations and alphanumeric format for output values. Be sure to describe what you
do and what the results are. *
(c) Once the function description has been entered, a simplified expression can be obtained by
selecting the “simplification” item from the Routine menu. Try it. This time, take the
defaults, which will produce a SOP form. Briefly describe what you did and what the results
were. Then repeat the simplification process, obtaining a POS form. Note that you must
make the window with the function description the active window in order to simplify the
function. Both POS and SOP forms should appear in the same output window and be
printed.
(d) Repeat steps (b) and (c) for the two functions XOR and XNOR together. Use A and B as
input variable names and F1 and F2 as output variable names. In the truth table, the output
values are listed as a combination, just like the input values. For example, the first line in the
truth table should be „00 01‟, since 0 XOR 0 = 0 and 0 XNOR 0 = 1. Now the output
window should contain both SOP and POS expressions for both F1 and F2 before printing.

3. Using the clock and counter parts in SimuAid
(a) Start SimuAid and use the menu help command to learn about the Parts menu, how to select
and place parts, and how to wire parts together to build a circuit. Also examine the
descriptions of the clock and counter parts.
(b) In a new circuit window (there is probably one window opened with a name similar to
Untitled), place a clock, a 2-bit counter, and a +V part. The 2-bit counter has two sections
(one on the left with the two output bits that indicate the count and one on the right with a
control output labeled K), two control inputs labeled En and CLR, and an unlabeled control

ECEN 1521L Exp 6 23-Aug-2011 06:44 AM                                                         Page 1 of 2
input with a wedge-shaped symbol at the input pin. This last control input is the clock input;
a pulse on the clock input causes the counter output to increment by 1.
To use this counter, wire the output of the clock part to the clock input of the counter. Also
wire the output of the +V part to both the En and CLR control inputs of the counter. To see
the signal values, select „Show I/O Values‟ from the View menu. The Reset (Ctrl-R) and Step
(Ctrl-T) items on the Simulate menu are used to control the operation of the counter. Try
pressing Ctrl-T several times and observe the values displayed on the circuit diagram. Note
that there is a button for Step as well. Also observe the effect of the Reset command (can you
find the Reset button?).
Starting from the reset condition, what is the counting sequence for this 2-bit counter? Notice
that this sequence can be used to provide all possible input combinations for a 2-input logic
circuit.
(c) As you are probably starting to learn, wiring circuits on a breadboard as well as drawing
diagrams of the circuit wiring can be a messy business! There is a nice help in SimuAid for
this problem. To see how it works, first disconnect the clock from the counter by deleting the
wires, and try the simulation again. You should find that nothing works: the counter needs a
clock input to function properly. Next, using the Label command (the ABC button), label the
clock output pin with the label “clk” and the counter clock input pin with the same label and
try the simulation again. You should find that it works as before. Now label the counter
outputs A and B with A on the left (the MSB). These signals will be used as logic circuit
inputs in the next step. Put Probes on each pin to see the values

4. Building and testing logic circuits in SimuAid
(a) Place the parts needed to build three different circuits for the XOR-function: a single XOR-
gate, an AND-OR circuit based on the SOP form from LogicAid, and an OR-AND circuit
based on the POS form. Note that you will need inverters to generate A' and B'. Use wires to
construct the two-level circuits and labels to connect the counter outputs to the circuit inputs.
(b) Single-step through the input combinations to test your circuit. Record your findings. Then
demonstrate your simulation to the instructor.

5. More XOR results
Using a 3-bit counter and only XOR-gates and inverters, build and test circuits that demonstrate the
following equations: (A  B)‟ = A‟  B and (A  B)  C = A  (B  C). Be sure to describe
how you do this “demonstration.”

REPORT: Keep a complete record of all data, results, observations, and answers to questions, written neatly and
legibly in ink on the front (unlined side) of standard engineering paper. Attach the lab sheet(s) as a cover and
number your pages in the upper right corner.
This is due at the beginning of the next lab period.

* Wherever possible, include printed examples of your computer work.
Be sure to label and write notes on such print-outs.

ECEN 1521L Exp 6 23-Aug-2011 06:44 AM                                                                      Page 2 of 2

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