write lab report for digital fundamental

EET 2210 Lab 7

Doing Binary Subtraction using Adders

Objectives:

1. To learn how binary subtraction can be done by using addition

Background: In class we talked about how to do binary subtraction by doing a standard

subtraction method. In microprocessors this process is not done by an iterative method

like we talked about in class but with a method that uses two compliments. Basically it

can be shown that by taking any negative numbers you have and then turn them into

twos compliments you can then turn the subtraction into addition.

Materials:

 2 7483 4 Bit Full Adders

 6 330 Ohm Resistors

 Dip Switches

 7404 Hex Inverter

Procedure:

1. It is probably best to read all of the procedure first and then start wiring.

2. Start be wiring your Dipswitch. You will need 6 inputs for this lab to create

two three bit numbers that you will then subtract from each other. Be sure

to wire one side of the switch to +5V and the other side have a 330 ohm

resistor going to ground.

3. You will now need to go through the process of taking 3 of your inputs and

turning them into a 4 bit twos compliment. Remember that the first step is

to generate an ones compliment, which is just flipping the bits. Use the 7404

to invert the three inputs that you choose. The forth bit will always be a one

from this process. The fourth bit can then just be +5V from the supply.

4. Once you have your three inverted bits and +5V from the supply you need to

wire one of the adders to add one to the result. Wire one of the adders

inputs to your four bit number and the other input wire to +5V and ground

so that the input it 0001. Remember that any unused inputs need to be tied

to ground.

5. Once the first adder is wired you will now wire the second adder. The three

inputs that you did not use before will be one input to this adder and the

output of the other adder will be the other input. Remember that unused

pins will be wired to ground.

6. Because of the number of inputs we can only use the digital channels of the

oscilloscope to view the output. Wire digital channels 0-3 to the second

adders S0-3 outputs and wire channel 4 to the carry out pin.

7. Have your instructor verify the operation of the circuit. This circuit will only

function correctly as long as the minuend is larger than the subtrahend. If

the subtrahend is larger than the minuend some weird stuff will start

happening (Basically make sure whatever numbers you put in the result is

positive).