2.1.4BINARY

ASCII

CHARACTER SETSA451: COMPUTER SYSTEMS AND

PROGRAMMING

HOW DOES A COMPUTER KNOW WHAT TEXT TO DISPLAY ON A SCREEN?

HOW MIGHT THIS BE DONE?

YOU ARE LEARNING..

•EXPLAIN THE USE OF BINARY CODES TO REPRESENT CHARACTERS

•KNOW THE TERM CHARACTER SET

•DESCRIBE WITH EXAMPLES (FOR EXAMPLE ASCII AND UNICODE) THE RELATIONSHIP BETWEEN THE NUMBER OF BITS

HOW MANY BITS WOULD YOU NEED TO CODE AN ENTIRE KEYBOARD?

• HOW MANY KEYS ARE THERE ON A NORMAL KEYBOARD?

THE CODE USED TO TRANSLATE LANGUAGE BETWEEN COMPUTERS AND PEOPLE IS CALLED

ASCII:

• IT IS PRONOUNCED ‘ASKEE’

ASCII IS SHORT FOR:

AMERICAN STANDARD CODE

FOR INFORMATION

INTERCHANGE

ASCII:

IS THE STANDARD CODE USED BY COMPUTERS

EVERYWHERE TO REPRESENT THE THINGS YOU CAN

TYPE USING THE KEYBOARD

ASCII CONVERSION TABLE:

IN ASCII THE WORD "CAT" WOULD BE:

• 1000011 1100001 1110100

YOU TRY

ON A BLANK SHEET OF PAPER, WRITE YOUR NAME

USING THE ASCII CHART, LOOKUP THE BINARY VALUES

FOR EACH LETTER AND WRITE IT DOWN IN A SERIES

DON’T FORGET THE SPACES BETWEEN YOUR LETTERS

GIVE YOUR ENCODED NAME TO A FRIEND

HAVE THEM DECODE THE CODE

HOW MANY BITS ARE REQUIRED TO STORE ASCII CODES?

• 8 BITS CAN STORE 256 CHARACTERS

• ENGLISH KEYBOARD USES 128 CHARACTERS WHAT ARE

THE OTHERS CODES USED FOR?

EXTENDED ASCII:

LANGUAGES SUCH AS

GERMAN, FRENCH, FINNISH, IRISH, ICELANDIC,

TAKE ADVANTAGE OF THE OTHER 128 SPACES TO INCLUDE THEIR

OWN SPECIAL CHARACTERS.

E.G. THE GERMAN UMLAUT Ü IS 11011100

THE TERM CHARACTER SET IS USED TO DESCRIBE A DIGITAL REPRESENTATION OF TEXT:

• ASCII IS THE MOST WIDELY USED CHARACTER SET

• THE ENTIRE COLLECTION OF CHARACTERS AVAILABLE IN A

SYSTEM SUCH AS ASCII IS CALLED A CHARACTER SET.

 OTHER CHARACTER SETS IN COMMON USE ARE:

EXTENDED ASCII (8 BITS – 256 CHARACTERS)

UTF-8 (8 BITS – 256 CHARACTERS)

UNICODE (16 BITS – 65536 CHARACTERS)

ASCII

•ASCII (AMERICAN STANDARD CODE FOR INFORMATION INTERCHANGE) IS THE MOST COMMON FORMAT FOR TEXT FILES IN COMPUTERS AND ON THE INTERNET.

• IN AN ASCII FILE, EACH ALPHABETIC, NUMERIC, OR SPECIAL CHARACTER IS REPRESENTED WITH A  BINARY NUMBER (A STRING OF 0S OR 1S).

•128 CHARACTERS ARE DEFINED.

CREATE AN ALTERNATIVE XMAS CARD

• USE YOUR KNOWLEDGE OF BINARY AND ASCII TO CONVERT AND WRITE A CHRISTMAS MESSAGE ON AN ALTERNATIVE CHRISTMAS CARD

• USE THE ‘ASCII’ CONVERTOR FOR THE TEXT

• USE THE HEXADECIMAL COLOUR PALLETE TO CODE A 16 X 16 GRAPHIC FOR THE FRONT OF THE CARD

THE COLOUR PALETTECode

Palette  

Colour Name R G B Hex

0000   Black 0 0 0 000000

0001   Maroon 128 0 0 800000

0010   Green 0 128 0 008000

0011   Olive 128 128 0 808000

0100   Navy 0 0 128 000080

0101   Purple 128 0 128 800080

0110   Teal 0 128 128 008080

0111   Silver 192 192 192 C0C0C0

1000   Gray 128 128 128 808080

1001   Red 255 0 0 FF0000

1010   Lime 0 255 0 00FF00

1011   Yellow 255 255 0 FFFF00

1100   Blue 0 0 255 0000FF

1101   Fuchsia 255 0 255 FF00FF

1110   Aqua 0 255 255 00FFFF

1111   White 255 255 255 FFFFFF