Sistemas Digitales I Number Systems and Codes parte

Sistemas Digitales I Number Systems and Codes (parte 2) Cristian Sisterna UNSJ - Argentina Sistemas Digitales I NUMBER SYSTEMS AND CODES 1

Binary Codes Sistemas Digitales I NUMBER SYSTEMS AND CODES 2

Binary Code For Decimal Numbers What is a Code? A set of n-bit strings in which different bit strings represent different numbers or other things A particular combination of n bit-values is called a code word Sistemas Digitales I NUMBER SYSTEMS AND CODES 3

Biniary Coded Decimal (BCD) One-hot Self-complementing Sistemas Digitales I NUMBER SYSTEMS AND CODES Error Detecting 4

BCD Addition of BCD digits is similar to adding 4 -bit unsigned binary numbers, except that a correction must be made if a result exceeds 1001. The result is corrected by adding 6 Sistemas Digitales I NUMBER SYSTEMS AND CODES 5

Code with mínimum bit change between code words Gray Code Sistemas Digitales I NUMBER SYSTEMS AND CODES 6

Gray Code Sistemas Digitales I NUMBER SYSTEMS AND CODES 7

Character Code A string of bits need not represent necessarily a number. Most of the information processed by computers is nonnumeric. The most common type of nonnumeric data is text, strings of characters from some character set. Each character is represented in the computer by a bit string according to an established convention. The most commonly used character code is ASCII (pronounced ASS key), the American Standard Code for Information Interchange. ASCII represents each character with a 8 -bit string, yielding a total of 256 different characters Sistemas Digitales I NUMBER SYSTEMS AND CODES 8

Character Code – The ASCII Code Sistemas Digitales I NUMBER SYSTEMS AND CODES 9

Codes for Detecting and Correcting Errors An error in a digital system is the corruption of data from its correct value to some other value An error is caused by a physical failure. Failures can be either temporary or permanent. Sistemas Digitales I NUMBER SYSTEMS AND CODES 10

Parity Method Error Detecting Sistemas Digitales I NUMBER SYSTEMS AND CODES 11

Codes for Serial Data Transmission v. Parallel Data v. Serial Data Transmission Sistemas Digitales I NUMBER SYSTEMS AND CODES 12

Codes for Serial Data Transmission Bit rate (bits per second, bps) Bit cell Synchronization signal Sistemas Digitales I NUMBER SYSTEMS AND CODES 13

Common Serial Data Transmission Codes NRZ + simplest and most reliable coding scheme for short distance transmission NRZI -Send Requieres clock signal to be sent a ‘ 1’ asaopposite of the level RZtoprevious along withduring the data define the bit waw sent the bit cell, Similar but the ‘ 1’ is cell and a ‘ 0 toas. NRZ, the same BPRZlevel transmitted half of the bit time. + clock can be recovered from NRZI Transmit three signal levels: +1, a 0, -1. +-coded Clock recovery can done with data long asbe the data does It’s similar toas. RTZ, but the ‘ 1’ are this type of transmitted data code, as as the not containg continous ‘ 0’ alternately aslong +1 and -1. data does not Manchester containg continous ‘ 0’ + DC balanced One transition per bit cell. + Very easy clock recovery Sistemas Digitales I NUMBER SYSTEMS AND CODES 14