C.S. Choy1 ITM1010 COMPUTER AND COMMUNICATION TECHNOLOGIES Prof. C.S. Choy, room 412 Prof. H.K. Tsang, room 306 Tutors: CY Poon ZJ Zhang CW Lee SK Cheung Assignments Mid-term Final

C.S. Choy2 FIRST-HALF TERM SCHEDULE Week (Monday) 8/1Introduction and Number System 15/1Logic Gates and Boolean Algebra 22/1Chinese New Year 29/1Conference Leave 5/2Digital Design 12/2Sequential Logic Design 19/2Computer Organization 21/3Mid-term Examination

C.S. Choy3 RECOMMENDED BOOKS Digital Electronics – A Simplified Approach by R.D. Thompson Prentice Hall The Digital Information Age by R. Kuc PWS Publishing

C.S. Choy4 INFORMATION SYSTEMS Process – amplifier, scanner, MP3 player Transmit – telephone network Store – tape and harddisk

C.S. Choy5 Why Digital (Binary System)? Information Integrity Better noise immunity Information Manipulation Computer is a binary system and its programmable characteristics offer the greatest flexibility

C.S. Choy6 SOURCES OF DIGITAL INFORMATION Analog Signal Representation of Number Values DecimalBinary

C.S. Choy7 BINARY NUMBER SYSTEM e.g. ( ) 2 =

C.S. Choy8 BINARY NOTATION Digit is called BIT. Possible representations: 1 0 highlow truefalse LSB – Least Significant Bit Bit change with the least effect HSB – Most Significant Bit Bit change with the most effect

C.S. Choy9 BINARY MATHEMATICS Addition = = Subtraction –Rules0 – 0 = 0 1 – 0 = 0 1 – 1 = 0 10 – 1 = 1

C.S. Choy10 BINARY MATHEMATICS Multiplication 1101 x 101 = x 5 10 = Division ÷ 101 = ÷ 5 10 =

C.S. Choy11 SIGNED BINARY NUMBER Ones (1s) Complement The 1s complement of a binary number of a binary number is derived by subtracting each bit in the number to be complemented from 1. e.g. 1s complement of 1100

C.S. Choy12 SIGNED BINARY NUMBER The use of complementary representation allows the subtraction process to be accomplished using addition. Positive result – high end-round carry Negative result – low end-round carry

C.S. Choy13 SIGNED BINARY NUMBER Twos (2s) Complement The 2s complement of a binary number is the 1s complement plus 1. Positive result – high carry Negative result – low carry

C.S. Choy14 SIGN BIT The use of a single bit, usually the leftmost bit to indicate the sign of a number. The meaning of the sign bit can be fixed arbitrarily. But normally, sign bit 0 - positive number 1 - negative number e.g = = 0101 Note: the magnitude of a number is represented by the lower three bits

C.S. Choy15 SIGN BIT 1s Complement2s Complement range: -7 – +7 range: -8 – +7 The leftmost bit still indicates sign. In complement representation, two numbers can be added or subtracted as usual. e.g. 6 + (-2)

C.S. Choy16 OVERFLOW CONDITIONS Overflow occurs whenever the sum of two positive numbers yields a negative result or when two negative numbers are summed and the result is positive. Overflow can be detected by the difference in the carry-in and carry-out of the sign bit.

C.S. Choy17 HEXADECIMAL

C.S. Choy18 BINARY-CODED DECIMAL BCD

C.S. Choy19 GRAY CODE

C.S. Choy20 AMERICAN STANDARD CODE FOR INFORMATION INTERCHANGE, ASCII The ASCII encodes the letters in the alphabet as well as numbers, it is an alphanumeric code. It is a 7-bit code so allows representation of 128 different characters and commands. upper-case and lower-case letters decimal numbers punctuation marks special symbols command codes for formatting text Extended ASCII 8-bit code allows for 128 additional graphics characters.