ASCII Code In 1963, in an effort to standardize data communications codes, the United States adopted
the Bell System model 33 teletype code as the United States of America Standard Code for Information
Exchange (USASCII)
EBCDIC Code The extended binary-coded decimal interchange code (EBCDIC) is an eight-bit fixed
length character set developed in 1962 by the International Business Machines Corporation (IBM)
BAR CODES Bar codes are those omnipresent black-and-white striped stickers that seem to appear on
virtually every consumer item in the United States and most of the rest of the world.
Discrete code. A discrete bar code has spaces or gaps between characters.
Continuous code. A continuous bar code does not include spaces between characters
Code 39 One of the most popular bar codes was developed in 1974
Universal Product Code The grocery industry developed the Universal Product Code (UPC) sometime
in the early 1970s to identify their products
ERROR CONTROL A data communications circuit can be as short as a few feet or as long as several thousand miles
Error detection is the process of monitoring data transmission and determining when errors have occurred.
Redundancy Checking Duplicating each data unit for the purpose of detecting errors is a form of error detection called
redundancy.
Vertical redundancy checking (VRC) is probably the simplest error-detection scheme and is generally referred to as
character parity or simply parity.
Checksum is another relatively simple form of redundancy error checking where each character has a numerical value
assigned to it.
Longitudinal redundancy checking (LRC) is a redundancy error detection scheme that uses parity to determine if a
transmission error has occurred within a message and is therefore sometimes called message parity
Cyclic redundancy checking. Probably the most reliable redundancy checking technique for error detection is a
convolutional coding scheme called cyclic redundancy checking (CRC).
ERROR CORRECTION Although detecting errors is an important aspect of data communications, determining what to
do with data that contain errors is another consideration.
Retransmission, as the name implies, is when a receive station requests the transmit station to resend a message (or a
portion of a message) when the message is received in error
Forward error correction (FEC) is the only error-correction scheme that actually detects and corrects transmission
errors when they are received without requiring a retransmission.
Hamming code will correct only single-bit errors
Character synchronization involves identifying the beginning and end of a character within a message.
Asynchronous Serial Data The term asynchronous literally means “without synchronism,” which in data
communications terminology means “without a specific time reference.”
Synchronous data generally involves transporting serial data at relatively high speeds in groups of characters called
blocks or frames.
POTS -plain old telephone system
DTE - data terminal equipment >can be virtually any binary digital device that generates, transmits, receives, or
interprets data messages
DCE - data communications equipment >is a general term used to describe equipment that interfaces data terminal
equipment to a transmission channel, such as a digital T1 carrier or an analog telephone circuit.
CSUs -channel service units (CSUs)
DSUs- digital service units (DSUs)
DCTE-data circuit-terminating equipment (DCTE)
Data modem is a DCE used to interface a DTE to an analog telephone circuit commonly called a POTS.
UART -universal asynchronous receiver/transmitter (UART)
USRT- a universal synchronous receiver/transmitter (USRT)
USART -universal synchronous/asynchronous receiver/transmitter (USART)
ACIA - asynchronous communications interface adapter (ACIA)
FEP -front-end processor
LCU – Line Control Unit
TBMT: transmit buffer empty.
RPE: receive parity error
RFE: receive framing error.
ROR: receiver overrun.
RDA: receive data available.
TSO –transmit serial data
SWE – Status Word Enable
RDA – Receive Data Available
RDE – Receive Data Enable
RDAR- Receive Data Available Reset
TDS – transmit data strobe
TEOC – Transmit end of character
CPU – Central Processing Unit
RCP – Receive Clock