Fundamentals of Computer Systems Project 1

Project 1 Introduction Virginia Tech

ECE 5484 Fundamentals of Computer Systems

Fall 2019

9/17/2019 Synchronous Session

What you need to do

1) Design a combinational logic circuit that displays the decimal value represented by a 4-bit Aiken code input according to the specifications given in the assignment.

2) Debug and test your design by simulating it using the Logisim simulator.

3) Document your work in a short report.

What you need to do

1) Design a combinational logic circuit that displays the decimal value represented by a 4-bit Aiken code input according to the specifications given in the assignment.

2) Debug and test your design by simulating it using the Logisim simulator.

3) Document your work in a short report.

Block diagram

Aiken Code to

Binary Code Converter

Y0

X1

X2

X3

X0 Y1

Y2

Y3

Hex Display

Code Definition

Decimal Digit

Aiken (2421) Code

(X3 X2 X1 X0)

Binary (8421) Code

(Y3 Y2 Y1 Y0) 0 0000 0000 1 0001 0001 2 0010 0010 3 0011 0011 4 0100 0100 5 1011 0101 6 1100 0110 7 1101 0111 8 1110 1000 9 1111 1001

Example

Conversion example

Aiken Code to

Binary Code Converter

Y0

X1

X2

X3

X0 Y1

Y2

Y3

Hex Display

Code for Decimal ‘7’: (X3, X2, X1, X0) = (1, 1, 0, 1)

(Y3, Y2, Y1, Y0) = (0, 1, 1, 1) = Decimal ‘7’

1

0

1

1

1

1

1

0

Basic design steps (a)

a. Create a truth table. – You need to reorder the input values so they are in

ascending order: 0000, 0001, 0010, …, 1111. – What about input values that are not specified, like 0101?

Treat them as “don’t care” conditions by making the outputs “X” (don’t care).

– One table with four output columns can be used for all four outputs. Or, you can create four separate tables.

Basic design steps (b-c)

b. Create four logic expressions: Y3, Y2, Y1, Y0. – You are not required to minimize the expressions, but the

circuit will be MUCH easier to draw in Logisim if you do. – You can easily minimize the expressions through

automation! See the Project 1 assignment for comments on online tools for minimization of Boolean functions.

c. Draw the logic circuit in Logisim based on the expressions.

Example: Expression for Y3 • Notice that bit Y3 is “1” if and only if X2 and X1

are 1 (X3 happens to also be a “1,” but this is not required.

• Thus, Y3 is:

• This much of the circuit is given in the starting circuit provided with the assignment

Y3 = X2 • X1

Logic Blocks for Four Outputs

Combinational Logic

X0 X1 X2 X3

Y0

Combinational Logic

X0 X1 X2 X3

Y1

Combinational Logic

X0 X1 X2 X3

Y2

AND Gate (X2•X1)

X0 X1 X2 X3

Y3

What you need to do

1) Design a combinational logic circuit that displays the decimal value represented by a 4-bit Aiken code input according to the specifications given in the assignment.

2) Debug and test your design by simulating it using the Logisim simulator.

3) Document your work in a short report.

The rest of the circuit

here

Modeling and Simulation Tips • Begin with the provided starter circuit • Test Y3 first by setting different values of

X3X2X1X0 and observing output Y3 – Change inputs by clicking on the X inputs – Observe logic values (bright green ⇒ “1”)

• Build and test the combinational logic for Y0, then for Y1, and, finally, for Y2

• Test the full system by observing specified versus actual decimal outputs for different input combinations

What you need to do

1) Design a combinational logic circuit that displays the decimal value represented by a 4-bit Aiken code input according to the specifications given in the assignment.

2) Debug and test your design by simulating it using the Logisim simulator.

3) Document your work in a short report.

Project 1: Report Content • Name, email, title at the top of page 1 • Body of the Report

– Section 1 – Objectives (What are you trying to do?) – Section 2 – Truth Table (Re-ordered version of table in

the assignment with all 16 input combinations) – Section 3 – Logic Expressions (What are the

expressions and how did you derive them?) – Section 4 – Circuit Design (Show the circuit from

Logisim) – Section 5 – Conclusions

• Cover the requested content, but keep it brief