Microsoft Word - Digital Logic Design v_4_6a

number of characters became an important competitive question. Up to that point, the language of

computer interfacing was English and to lesser extend other western languages that have less than

256 characters. The ASCII code could represent them using its 8-bit word with 256 unique codes.

But this is not true for a number of Asian languages.

In order to meet the need for the larger Asian languages character set and maintain compatibility

with ASCII code, Unicode was introduced. Unicode use 16 bits, so it is capable of representing as

many as 2^16 or 65,536 unique symbols. The majority of today’s computers use Unicode which is also

referred to as the double byte code.

 Other Binary Codes

 Binary coded decimal (BCD)

BCD assigns 4 binary bits to each binary digit. The only drawback is that only 0 to 9 are used,

and the other 6 combinations from 10 to 15 are not used.

 Reflective Gray Code (RGC)

RGC is a binary number system organized so that consecutive codes in the sequence only

require one bit change as shown below:

2-bit Reflective Gray Code

00

01

11

10

3-bit Reflective Gray Code

000

001

011

010

110

111

101

100

Binary Coded Decimal

0000  0

0001  1

0010  2

0011  3

0100  4

0101  5

0110  6

0111  7

1000  8

1001  9