EE171

Electrical Engineering Department
Portland State University
Portland, OR

DESIGN PROJECT #1

Problem Description:

In digital computers, letters of the alphabet and the ten decimal numerals can be coded in the form of unique combinations of five or six bits. One of these codes is the 6-bit Flexowriter code, which is used for some punched paper tape. A code similar to this is given below in terms of octal equivalents.
Character Codes

A 14       0 05
B 56       1 74
C 70       2 65
D 22       3 61
E 04       4 27
F 62       5 07
G 46       6 47
H 24       7 76
I 50       8 45
J 32       9 25
K 72 
L 26   All character codes are in Octal.  To convert the octal 
M 16   code to its six bit equivalent, convert each digit (octal) 
N 60   to its three digit binary equivalent:
O 44   
P 34      For example, B = 56 = 101 110 = 101110
Q 52                             5   6 
R 30
S 42
T 10   To convert each octal code to its decimal equivalent,  
U 54   multiply each digit by its decimal weight.
V 64  
W 12      For example, B = 56 = 5x8 + 6x1 = 40 + 6 = 46
X 66
Y 36
Z 06

Your job is to design a circuit which detects whether a code on six data lines represents a number, a letter, or an illegal code. The circuit should produce three output signals, A, N, and E, as shown below.

A   N   E

1   0   0   Alphabetic character sensed

0   1   0   Numeric character sensed

X   X   1   Illegal character sensed  (X = don't care)

Documentation

Your documentation should consist of two separate entities, the log book and the formal report.

Log book

This is an "as you go" write up of the project. Include an ongoing record of your thought process and attempts as you develop a design, with DATED ENTRIES. This must include all "false starts" as well as successful paths. It must be written "as you go," not "after the fact" as is usually done with, for example, physics lab reports. It should be written in a manner such that any engineer could read the lab book and understand your design. Thus, explanations as to what you are doing are necessary during this stage of the write up. Please see your instructor or TA if you have questions about the logbook. The following sequence of steps should be performed and documented in your lab book.

Develop a complete truth table for the problem.
Use Karnaugh maps to produce the active low and active high minimal sum of products expressions for each of the three outputs.
Factoring the expressions as possible.
Design a circuit which implements the expressions using only 2, 3, 4, and 8 input NAND gates and inverters. You are to use a maximum of 7 IC packages. This problem has been solved with five IC's. Also note that while your grade on this project is not determined by the number of chips used, it is a factor in your grade on project 2.
Analyze the chip count for your final design, reduce the number of IC's if possible.
Draw a schematic with Mentor's Design Architect.
Go through an analysis to show that the circuit will work. This is done without going through all values in the Truth Table to determine if it works. This is done by carrying the expressions through the circuit. (See Chapter 5 for help.)

Formal report

The formal report is a document that will be written at the end of the project. It will be done "nicely". In fact, think of this as your presentation of the project. It is suggested, but not required, that you type your report. Include the following sections in your report.

Introduction - Describe the problem and your proposed solution.
Design - Describe the process that you used to design your solution and show your final design. Include your final Boolean expressions and Mentor Graphics Schematic. You don't need to show your entire truth table and all your Karnaugh maps in the formal report (they should be in your log book), but you may want to show a sample K-map as you explain your design process.
Analysis - Justify the chip count for your design and discuss the process that you went through to verify that the circuit works.
Conclusion - Summarize your work -- review the problem and your solution and discuss what you learned.
Include the following signed "intellectual property" statement:

I do hereby affirm that I designed this circuit by myself.

    Signed __________________________________  Date _______________

To receive credit you must do this project yourself and include the signed statement!