1. NUMBER SYSTEM AND COMPUTER CODES Chapter 2

2. Prelude Fingers, sticks, and other things for counting were not enough! Counting large numbers Count in groups Evolution of the number system

3. Number systems A set of values used to represent quantity Non-Positional Number Systems count with their fingers, stones and pebbles difficult to perform arithmetic operations No zero, difficult to calculate large numbers E.g. the Roman number system Positional Number Systems Finite number of symbols to represent any numbers Symbol and it’s position defines a number Decimal, binary, octal, hexadecimal

4. ASCII- American standard for Information Interchange

5. Base or radix Number of unique digits

6. Number Systems - Decimal The decimal system is a base-10 system. There are 10 distinct digits (0 to 9) to represent any quantity. For an n-digit number, the value that each digit represents depends on its weight or position. The weights are based on powers of 10. 6 1024 = 1*10 3 + 0*10 2 + 2*10 1 + 4*10 0 = 1000 + 20 + 4

7. Number Systems - Binary The binary system is a base-2 system. There are 2 distinct digits (0 and 1) to represent any quantity. For an n-digit number, the value of a digit in each column depends on its position. The weights are based on powers of 2. 7 1011 2 = 1*2 3 + 0*2 2 + 1*2 1 + 1*2 0 =8+2+1 =11 10

8. Number Systems - Octal Octal and hexadecimal systems provide a shorthand way to deal with the long strings of 1’s and 0’s in binary. Octal is base-8 system using the digits 0 to 7. To convert to decimal, you can again use a column weighted system 8 10 7512 8 = 7*83 + 5*82 + 1*81 + 2*80 = 3914 10 82 An octal number can easily be converted to binary by replacing each octal digit with the corresponding group of 3 binary digits 7512 8 = 111101001010 2 8

9. Number Systems - Hexadecimal Hexadecimal is a base-16 system. It contains the digits 0 to 9 and the letters A to F (16 digit values). The letters A to F represent the unit values 10 to 15. This system is often used in programming as a condensed form for binary numbers (0x00FF, 00FFh) To convert to decimal, use a weighted system with powers of 16. 9

10. Example- Value of 2001 in Binary, Octal and Hexadecimal 10

11. Example- Conversion: Binary  Octal  Hexadecimal 11

12. Converting decimal to binary, octal and hexadecimal To convert from decimal to a different number base such as Octal, Binary or Hexadecimal involves repeated division by that number base Keep dividing until the quotient is zero Use the remainders in reverse order as the digits of the converted number 12 Repeated Divide by 2

13. Base N to Decimal Conversions Multiply each digit by increasing powers of the base value and add the terms Example: 10110 2 = ??? (decimal) 04/03/10 CPE1002 (c) Monash University13

14. Binary Addition Similar to decimal operation Leading zeroes are frequently dropped. 4 Possible Binary Addition Combinations: (1) 0(2) 0 +0 +1 00 01 (3) 1(4) 1 +0 +1 01 10 Sum Carry Ex 1,2,3 For Exam

15. Binary Subtraction Just like subtraction in any other base Minuend 10110 Subtrahend -10010 Difference 00100 And when a borrow is needed. Note that the borrow gives us 2 in the current bit position. Ex 1,2 For Exam

16. And a full example And more ripple -

17. Octal/Hex addition/subtraction 17 Octal Addition 1 1 1 Carries 5 4 7 1 Augends + 3 7 5 4 Addend 11445 Sum Octal Subtraction 6 10 4 10 Borrows 7 4 5 1 Minuend - 5 6 4 3 Subtrahend 1 6 0 6 Difference Hexadecimal Addition 1 0 1 1 Carries 5 B A 9 Augend + D 0 5 8 Addend 1 2 C 0 1 Sum Hexadecimal Subtraction 9 10 A 10 Borrows A 5 B 9 Minuend + 5 8 0 D Subtrahend 4 D A C Difference

18. BCD Binary-coded decimal, or BCD, is a method of using binary digits to represent the decimal digits 0 through 9. A decimal digit is represented by four binary digits … The binary combinations 1010 to 1111 are invalid and are not used.

19. ASCII Code "ask-key“- common code for microcomputer Standard ASCII character set 128 decimal numbers ranging (0-127) Assigned to letters, numbers, punctuation marks, and the most common special characters. The Extended ASCII Character Set also consists of 128 decimal numbers (128-255) representing additional special, mathematical, graphic, and foreign characters. Groups of 32 characters

20. EBCDIC - Extended Binary Coded Decimal Interchange Code It is an 8 bit character encoding Used on IBM mainframes and AS/400s. It is descended from punched cards The first four bits are called the zone category of the character Last four bits are the called the digit identify the specific character There are a number of different versions of EBCDIC, customized for different countries.

21. Assignments IOA, IA, GA, Case !@#$

22. Chapter 122 Binary Multiplication Division 1 1 0 1 0 Multiplicand x 1 0 1 0 Multiplier 0 0 0 0 0 1 1 0 1 0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 1 0 0 Product