Chapter 6

Current transmission codes

ASCII and EBDIC

Code 39 definition

An Alphanumeric barcode consisting of 43 characters; the 26 alphabetical characters, 10 numeric characters, 10 numeric characters, and 7 special characters.

CCITT

Consultative Committee for International Telephony and Telegraphy.

Check Character

In a UPC Barcode, the last or 12th digit used for error detection when the barcode is scanned.

Examples of transmission codes

International Morse Code, and Baudot

SUB

Substitute is interpreted the same as CAN

Start Bit

The first bit used to frame an asynchronously transmitted character. The start bit is always a logic 0 or space.

Base of Hex or Hexidecimal system

16 characters: 0 through 9 and A through F

Universal Product Code (UPC) definition

A 12-digit numerical bar code adopted by the National Association of Food Chains. UPC is most commonly found on grocery items.

Baudot

A 5-bit alphanumeric code used in telegraphy and radio teletype (RTTY)

ASCII (American Standard Code for Information Interchange)

A 7-bit alphanumeric code used extensively in data communications. A parity bit is often added to the 7-bit code for error detection.

Excess - 3 Code

A BCD code is similar to 8-4-2-1 code, except that 3 is added to the decimal number before it is encoded into a 4-bit word.

Hexadecimal number system

A Computer numbering system widely used as shorthand to represent groups of 4 bits (1 hexadecimal character). There are 16 valid characters in this number system (0 through 9 and A through F).

PostNet(Postal Numeric Encoding Technique)

A bar code developed by the U.S Postal service to increase the sorting speed, delivery, and accuracy of mail based on ZIP Codes.

Binary Coded Decimal

A binary code used to express a decimal number with 4 binary bits. BCD is referred to as 8-4-2-1 code due to the binary weighting of each of the 4 bits.

Octal Number System definition

A computer numbering system widely used as shorthand to represent groups of 3 bits (1 octal digit). There are 8 valid digits in this number system (0-7).

Morse Code definition

A digital code made of a series of dots and dashes used to represent alphanumeric characters, punctuation and control.

Exclusive-OR definition

A logic function that compares two binary bits and is true when the two bits do not equal each other (1 and 0 0r 0 and 1) and false when they do (0 and 0 or 1 and 1).

Bar Codes

A series of consistently sized white and black bars on items for identification. The black and white bards, and their widths in some codes, represent binary 1's and 0's.

Extended Binary Coded Decimal Interchange Code (EBCDIC)

An 8 - bit alphanumeric code (no parity) developed by IBM for synchronous communications with mainframe computers and peripheral devices

Delivery Point Bar Code (DPBC)

An extension of the POSTNET bar code. The DPBC adds two more digits to the 9-digit ZIP+4 to represent the last two digits of a street number or P.O. Box number.

Unweighted Code definition

Any code whose bits do not have numeric weighting

Computer Number Based Systems include

Binary (base 2), Octal (Base 8), Hexadecimal (Base 16)

CAN

Cancel is used to suspend or terminate an escape or control sequence. An error character is typically displayed on the screen.

Control Characters definition

Characters used to control the format and transmission flow of data over a telecommunicatitons channel

ASCII four device control characters

DC1, DC2, DC3, DC 4

Classifications of Control Characters

Device control, format effectors, information separators, transmission control

ESC:

Escape is an ASCII character used for sending special command and control functions. ESC, followed by a single character or string of characters, is called an escape sequence. Escape sequences are used to perform special functions, such as cursor positioning, clearing the screen, and editing of text.

Disadvantages of Bar Code

Extra equipment required, computer system and special application software may be required, primary used is for fixed, repetitive data input, not for variable data input.

Advantages of a Bar Code

High throughput, Increased productivity, Low Cost, Little Operator training, High Data accuracy, Readable by contact and noncontact scanners

Decimal number system explained

In simple terms, the base of a numbering system is the numeric value that is raised to an exponent or power equal to another number. Raising any number-system base to an incrementing exponent gives us the weightings of the significant digits of which a number is compromised.

Start Guard Pattern's use

Marks the beginning of a 12-digit UPC bar code. The two long black bars separated by a white bar (logic 101), on a UPC label can readily be identified at the beginning of the bar code.

PSTN

Public Switched Telephone Network

SI

Shift in is used to return to the normal ASCII character set

SO

Shit out is used to shift out of the normal ASCII character set and into an extended character set. The extended character set may include graphic symbols, mathematical symbols, and so on.

The Decimal Number System

The base 10 numbering system with which we are most familiar. There are 10 valid digits in base 10 (0 through 9).

Binary Number System

The base 2 system is widely used to represent digital logic circuits in computers and electronics involving signaling with two states. There are two valid digits in binary (0 and 1).

LSB definition

The binary bit with the least significant weighting in a binary number

MSB definition

The binary bit with the most significant weighting in a binary number

UPC Number System Character

The first of 12 digits on a UPC bar code that identifies how the UPC symbol is used (e.g. a coupon, regular sales item).

Grouping

The grouping of binary bits to represent other characters in other number systems. For example, 3 bits equals one octal character, and 4 bits equals one hexadecimal character.

Stop Bit

The last bit used to frame an asynchronously transmitted character. The stop bit is always a logic 1 or Mark.

Baud Rate

The rate at which a signal is changed or modulated. Baud rate is directly related to the number of bits transmitted per second.

Binary Voltages explained

Used by laptops, desktops, peripheral devices, and all electronic devices use _____. is it the combination of 1's and 0's representing the two distinct binary states of voltage or current that are encoded and decoded into the information we utilize.

states of voltage explained

Voltage is a representation of the electric potential energy per unit charge. If a unit of electrical charge were placed in a location, the voltage indicates the potential energy of it at that point. In other words, it is a measurement of the energy contained within an electric field, or an electric circuit, at a given point.

BEL

When the BEL character is received by a terminal or computer an audible response is given. Its purpose is to gain the attention of the operator

Gray Code definition

an unweighted code that provides a single bit change between successive counts. Gray code reduces switching noise and bit errors.

Uses of Information separators

are used as delimiters in the organization of file transfers.

Format Effectors explained

are used to control a video display terminal (VDT) cursor movement or the positioning of a printing head on a printer. This allows an operator to control the physical layout of printed material.

rudimentary

basic, introductory, fundamental

Eight bits is equal to a

byte

FS File Separators use

contains the groups of data.

GS - Group Separator use

delimits a number of records contained in the group

RS record separator use

delimits a record of information that contains so many units

Unit Separator use

delimits the smallest unit of information within the file.

EM End of medium use

is to indicate the end of a file transfer when different storage mediums are used.

Octal Number System

is used in conjunction with some microprocessors, computers, and their respective assembly language instruction sets. This is because their internal architectural design is conveniently described in groups of three binary bits.

Decimal Number System Continued

the base of any number system also tells us the maximum number of valid characters that can be used to represent any number within that system. Because the DNS has a base of 10, there are 10 valid characters, 0 through 9 .

Bit

the logical value of each character or digit, whether it is a 1 or a 0 is called a ______

NULL

the null byte is a string of zeros that is used as a programming and test aid. It is often used to identify the end of a string of text. It is also used as a redundant byte to fill memory.

Flow Control definition

the process of regulating the flow of data from one point to another using DC1 (XON) and DC3 (XOFF) ex: computer sending a long text file to a printer

Binary electrical impulses

these pulses take on one of two states: a logic 0 or a logic 1. EX: 0 V is a logic 0 and +5 V is a logic 1.

Octal and Hexadecimal number systems and their relationship to computers

these two number systems are used primarily as a form of shorthand to represent groups of binary bits or large strings of binary numbers.

delimit

to limit the boundaries of

10 Transmission Control characters use

used for flow control and framing blocks of data