ELT-217, Experiment AD-4: ADDERS and ALU

OBJECTIVE:To investigate the performance of Adder Circuits both using individual gates and an MSI IC.

EQUIPMENT NEEDED:2 ea. - 7400 Quad NAND IC1 ea. - 7486 Quad XOR IC1 ea. - 74LS181 ALU IC(optional) 1 ea. 7404 hex inverter.Analog DiscoveryComputerbreadboard and wire as needed

GENERAL:

Before actually wiring, make a schematic diagram showing which virtual switch and/or virtual

LED is connected to what; show all connections and pin numbers. It is strongly recommended

that you arrange all switches and LEDs so that they are in order, on the same line, with the

MSB at the left and LSB on the right. Include clearly labeled diagrams in your report for each

different set-up.

PROCEDURE:

Part 1 Using individual gates.

Construct an adder able to add two 2-bit numbers from a half-adder and a full adder built

using only XOR and NAND gates. Your test book should show a logic diagram for this 2-bit

adder. In your report explain clearly the logic functions occurring and why this has the

proper function. Use Three of your virtual LED's to observe the outputs and four virtual

data switches to control the inputs. Show in your report a complete wiring diagram,

including pin numbers and AD2 connections.

The adder should be able to add two 2-bit binary numbers, A and B, consisting of A1A0 &

B1B0 to get a 3-bit sum consisting of Sum1, Sum0, and the carry Cout. In other words:

A1 A0

+ B1 B0

-----------------Cout Sum1 Sum0

Verify that your adder is working properly by testing all 16 possible input combinations of

numbers A & B. Also show a block diagram in your report of how you could connect half

and/or full adders (as blocks) to add one four-bit number to another four-bit number. Figure

out how many gates you would need to actually implement your block diagram.

Take a “screen shot” of any one set of data and include it in your report. In your report be

sure you clearly indicate which set of data is being tested and the meaning of each relevant

switch and LED.

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Experiment AD-4

Part 2 Using a single MSI I.C., General

Use the 74LS181 adder to construct an adder capable of working with two 4-bit binary

numbers. Show the wiring diagram clearly in your report. Use eight virtual switches for the

data inputs. Use five virtual LEDs to show the states of the four Function Outputs and the

Carry Output (Cn+4). Use two of the remaining virtual data switches to control the Mode

Control input (M) and the Carry Input (Cn) as needed for each part of your investigation.

Wire the Function Select inputs (S3-S0) either high or low by wiring each of them directly to

+5 or ground as required for each part. [Optionally, if available, use the virtual switches of

a second AD2 (connected to a second computer) for the Function Select inputs (S3-S0). In

that case, be sure to connect the grounds of the two AD2s.]

(optional) Wire an inverter between the Cn switch and the Cn input. Also an inverter between

the Cn+4 output and the Cn+4 LED. This will make the switches & LED indicate directly.

2A) Addition: Verify the positive-logic addition operation of the 74LS181 by setting M=0 and

using at least 6 different sets of data (each with both a carry in and no carry in) for

binary addition problems (A plus B), at least 2 of which will generate a carry. In other

words, for each set of the 6 sets of data there should be 2 answers, one with a carry in and

one without a carry in. The data used can be of your choosing but should be non-trivial –

For example you should not use one or both numbers =0. Note that Cn and Cn+4 use

inverted logic compared to the rest of the signals unless you have added the optional

inverters.

Take a “screen shot” of any one set of data and include it in your report. In your report

clearly indicate what set of data is being tested and the meaning of each switch and LED.

2B) Logic Operations: Verify the positive-logic logical operation with M=1 by doing do at least

3 different non-trivial logic operations each using several (3 or 4) sets of data for each type

of operation. Choose whatever operations from the list of logic operations (with M=1) you

feel are appropriate. The data used should be of your choosing but should be non-trivial.

(For example you should not choose the output to equal one of the numbers, ignoring the

other number, you should not choose one or both numbers equal zero; and you should not

choose both numbers to be the same.) In your report show clearly the setting of all of the

Function Select and Mode inputs for each operation as well as the status of all inputs and

outputs. For each test explain clearly what function is being tested and how you verified it.

Take a “screen shot” of any one set of data and include it in your report. In your report

clearly indicate which set of data is being tested and the meaning of each switch and LED.

In your report comment on the differences in using a more versatile MSI chip in place of wiring

individual gates. 11/6/17 – dw

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Experiment AD-4

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Experiment AD-4

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