1. Binary Codes
Computers and other digital systems "work" with binary numbers.
I/P & O/P is usually done using decimal numbers, alphabetics, special symbols.
Some way of representing alphanumerics with binary numbers is required.
These representations are called codes.
Many codes are possible, and a few standard codes are used, such as:
ASCII - American Standard Code for
Information Interchange  
EBCDIC - Extended Binary Coded Decimal
Interchange Code   
BCD - Binary Coded Decimal. For numbers only.  
Hardware and/or software is required to convert coded numbers into binary numbers before any arithmetic operations can take place.
7-bit System
Used in Big Mainframe Systems

2. Alphanumeric Character codes
Character 6-bit internal code ASCII code bit EBCDIC A B C D E F G H I J
…………
…………………

3. ASCII 7-bit Codes

4. Binary Codes for Decimal Numbers
Weighted codes: 8421, 6311, Excess-3
Non-weighted codes: 2-out-of-5, Gray

5. Binary Codes for Decimal Numbers (cont.)
BCD - Convert decimal numbers to binary code, digit by digit
(at least bits required).
8421 code:
6311 code: 925
(for each decimal digit) 9 5 1 6
By looking up the previous table

6. The Meaning of Data 5012110 C I 9096 ??? Meaningless, why???
e.g.: Consider the following 16-cell register
If one assumes that the content of the register represents a binary integer, the decimal number is: =
If one assumes an 8-bit EBCDIC code, the two characters are:
In excess-3 code:   
In BCD code:
The same bit configuration may be interpreted differently for different types of elements of information. The computer must be programmed to process this information according to the type of information stored.
C I
9096
???
Meaningless, why???

7. Boolean Algebra
George Boole ( ) applied a set of symbols to logical operations.
Digital electronics applies his set theory and logic to (binary) switching networks.
Binary number system is used to represent the two possible states of our systems.
 The symbols 0 & 1 are used to represent:
  True or False
  Flow or No Flow
  Open or Closed
  Voltage1 or Voltage2
  etc.
word statements
currents, fluids
switches, doors, etc.
anything with 2 states

8. Boolean Algebra Deals with manipulation of Variables & Constants
Boolean Variables, such as X, Y, Z, A, B, C, etc. can have "values" of either 0 or 1.
 0 & 1 are constants & are symbols only, representing two different states of a quantity.
i.e.
F or T
Low voltage or high voltage, usually written L or H
Flow or not flow
e.g. 0V  logical 0
+5V  logical 1
or 0V  1
+5V  0
+ ve logic
- ve logic

9. NOT (compliment or invert) AND OR
Basic Operations
NOT (compliment or invert)
AND OR
Only 3
e.g. Not 1 is written as:
Not :
  X and Y :
  X or Y :
  1 or X :
 If the variables represent voltages of the I/P or O/P of a switching network, we symbolically represent these operations by:
NOT
If O/P is called C, we write:
1´ or 1
X ´ or X
X • Y
X + Y
1 + X
inversion symbol or “bubble
C = X´

10. Boolean Operations (cont.)
AND OR
where values for X, A, B, C are They actually correspond to two different voltage levels when realized electronically.
e.g.
Characteristics of
an Inverter B
0 or 1
0 & 5V; V & 0V, etc.
Truth Table
X C
if X = 0 C = 1
if X = 1 C = 0

11. Boolean Operations (cont.)
AND gate A B C A B
C = A ● B
Logical Multiplication
OR gate A B C A B
C = A + B 1 1
Logical Addition 1
Also called Inclusive OR 1 1