9/11/08
ESE218 Fall 2008 Lecture 4
1
ESE218 Lecture 4. Error detection and correction.
Introduction to switching algebra. Logic gates
Outline
ASCII
Error detection and correction
Parity bit
Distance
Introduction to Hamming codes
Introduction to switching algebra
Operators and operator precedence
Functions of two variables
Logic operations and gates
AND, OR, NOT
NAND, NOR
XOR, XNOR
parity generation and checking
Gray-to-binary code conversion
Propagation delay
Summary

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9/11/08
ESE218 Fall 2008 Lecture 4
2
A
merican
S
tandard
C
ode for
I
nformation
I
nterchange (æski)
The American Standards Association (ASA, later to become
ANSI
)
first published ASCII as a standard in 1963
5-bit
7-bit
HEX form:
0D=
0
0001101
MSB=0 for all
=>128 codes
An upper case character can be changed
to the corresponding lower case character
by changing a single bit: 01
0
0 -> 01
1
0