2. Coding of Information Assign a unique string of binary digits to each piece of information There are many standard coding groups –Decimal Codes (BCD – Binary Coded Decimal) Ways to encode the first 10 symbols of the decimal number system. –Unit-Distance Codes Only one bit changes between succesive values –Alphanumeric Codes Ways to encode characters and numeric data

3. BCD Codes To represent the first 10 digits in decimal (0-9), how many bits are needed? –With 3 bits, there are 8 different combinations –With 4 bits, there are 16 different combinations Since only 10 different combinations are needed, use 4 bits – 6 combinations will not be used.

4. Weighted Decimal Codes Decimal Digit8421 Code2421 Code5421 Code7536’ Code 00000 10001 1001 20010 0111 30011 0010 40100 1011 50101101110000100 60110110010011101 70111110110101000 8 111010110110 91001111111001111

5. BCD Codes (Decimal Codes) Weighted Code –8421 code Most common Default The corresponding decimal digit is determined by adding the weights associated with the 1s in the code group. **** The BCD representation is NOT the binary equivalent of the decimal number ***** –623 10 = 0110 0010 0011 –2421, 5421,7536, etc… codes The weights associated with the bits in each code group are given by the name of the code

6. BCD Codes (Decimal Codes) Nonweighted Codes –2-out-of-5 Actually weighted 74210 except for the digit 0 Used by the post office for scanning bar codes for zip codes Has error detection properties

7. Unit Distance Codes Important when an analog quantity must be converted to a digital representation. Only one bit changes between two successive integers which are being coded.

8. Unit-Distance Codes (Gray Code) Decimal DigitGray Code Decimal DigitGray Code 00000 81100 10001 91101 20011 101111 30010 111110 40110 121010 50111 131011 60101 141001 70100 151000

9. Alphanumeric Codes Codes to handle alphabetic and numeric information, special symbols, punctuation marks, and control characters. ASCII (American Standard Code for Information Interchange) is the best known. Unicode – a 16-bit coding system provides for foreign languages, mathematical symbols, geometrical shapes, dingbats, etc…

10. b6b5b4b6b5b4 b3b2b1b0b3b2b1b0 000001010011100101110111 0000NULDLESP0@P`p 0001SOHDC1!1AQaq 0010STXDC2"2BRbr 0011ETXDC3#3CScs 0100EOTDC4$4DTdt 0101ENQNAK%5EUeu 0110ACKSYN&6FVfv 0111BELETB‘ 7GWgw 1000BSCAN(8HXhx 1001HTEM)9IYiy 1010LFSUB*:JZjz 1011VTESC,;K[k{ 1100FFFS,<L\l| 1101CRGS- M]m} 1110SORS. >N^n~ 1111SIUS/ ?O_oDEL ASCII Code

11. UNICODE UNICODE is a 16-bit code for representing alphanumeric data. With 16 bits, can represent 2 16 or 65536 different symbols. 16 bits = 2 Bytes per character. $0041-005A A-Z $0061-4007A a-z Some other alphabet/symbol ranges $3400-3d2d Korean Hangul Symbols $3040-318F Hiranga, Katakana, Bopomofo, Hangul $4E00-9FFF Han (Chinese, Japenese, Korean) UNICODE used by Web browsers, Java, most software these days.BR 2/00

12. Error Detection and Error Correction Codes

13. How Much Memory? Memory is purchased in bits – –How many bits do I need if I want to distinguish between 8 colors? –How many bits do I need if I want to represent 16 million different colors?

14. How Much Memory? How many bits do I need if I want to distinguish between 8 colors? 2 x-1 < 8 <= 2 x x = 3 (3 bits are needed) How many bits do I need if I want to represent 16 million different colors? 2 x-1 < 16 million <= 2 x 16M = 1Mx16 = 2 20 x2 4 = 2 24 x = 24 (24 bits are needed)

15. What do you need to know? Codes (Binary, Weighted BCD (8421 Code), Alphanumeric (ASCII), Unit Distance(Gray)) Number of bits needed?