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ASCII - An acronym for American Standard Code for Information Interchange. ASCII files are plain, unformatted text files that are understood by virtually any computer. Windows Notepad and virtually any word processor can read and create ASCII files. ASCII files usually have the ".TXT" extension (e.g., README.TXT).


Binary File - A file that contains data or program instructions written in ASCII and extended ASCII characters.


Bit - A binary digit in the binary numbering system. Its value can be 0 or 1. In an 8-bit character scheme, it takes 8 bits to make a byte (character) of data.


Bytes - A collection of eight bits that represent a character, letter or punctuation mark.


Cable - Transmission medium of copper wire or optical fiber wrapped in a protective cover.


Client/Server - A networking system in which one or more file servers (Server) provide services; such as network management, application, and centralized data storage for workstations (Clients).


COM port - Short for a serial communication port. Most serial communication software communicates with a computer through a communication port, and most IBM and IBM-compatible computers support up to four serial ports COM1, COM2, COM3, and COM4. Additional ports can be added by adding additional hardware.


Data bits - A group of bits (1's and 0's) that represents a single character or a byte. Typically, there are seven or eight data bits. During an asynchronous communication (e.g., BitCom connecting to CompuServe), each side must agree on the number of data bits. Data bits are preceded by a start bit and followed by an optional parity bit and one or more stop bits.


DA - data access.


DNS (Domain Name System) - A DNS server lets you locate computers on a network or the Internet (TCP/IP network) by the domain name. The DNS server maintains a database of domain names (hostnames) and their corresponding IP addresses. The IP address "", corresponds to the DNS name www.google.com.


Flow control - A method of controlling the amount of data that two devices exchange. In data communications, flow control prevents one modem from "flooding" the other with data. If data comes in faster than it can be processed, the receiving side stores the data in a buffer. When the buffer is nearly full, the receiving side signals the sending side to stop until the buffer has space again. Between hardware (such as your modem and your computer), hardware flow control is used; between modems, software flow control is used.


Handshaking - is how the data flow between computers/hardware is regulated and controlled. Two distinct kinds of handshaking are described: Software Handshaking and Hardware Handshaking. An important distinction between the kinds of signals of the interface is between data signals and control signals. Data signals are simply the pins which actually transmit and receive the characters, while control signals are everything else.


Internet - A global network of networks used to exchange information using the TCP/IP protocol. It allows for electronic mail and the accessing ad retrieval of information from remote sources.


IP, Internet Protocol - The Internet Protocol, usually referred to as the TCP/IP protocol stack, allows computers residing on different networks to connect across gateways on wide-area networks. Each node on an IP network is assigned an IP address, typically expressed as 'xx.xx.xx.xx'.


IP address (Internet Protocol address) - The address of a computer attached to a TCP/IP network. Every client and server station must have a unique IP address. Client workstations have either a permanent address or one that is dynamically assigned to them each dial-up session. IP addresses are written as four sets of numbers separated by periods; for example,


LAN (Local Area Network) - A network, connecting computers in a relatively small area such as a building.


NIC, Network Interface Card - A card containing the circuitry necessary to connect a computer to a particular network media. Typically, the NIC plugs into the computer's accessory bus, (PCI, USB, etc.) and provides a network connection such as 10baseFL (fiber Ethernet), thin-net, AUI, etc.



OPC (OLE for Process Control) - a set of universally accepted specifications providing a universal data exchange mechanism in control and management systems.


OPC Alarms and Events - the OPC interface for access to alarm and event data.


OPC Data Access - the OPC interface for access to real-time data.


OPC DA - see OPC Data Access.


OPC Historical Data Access - the OPC interface for access to archived data.


OPC HDA - see OPC Historical Data Access.


PC - abbreviation for a Personal Computer.


Parity - In data communications, parity is a simple procedure of checking the integrity of transmitted data. The most common type of parity is Even, in which the number of 1's in a byte of data adds up to an even number, and None, in which a parity bit is not added.


Ports - is a connection point for a cable.


Protocol - is a formal description of a set of rules and conventions that govern how devices on a network exchange information.


RS232, RS423, RS422, AND RS485 - The Electronics Industry Association (EIA) has produced standards for RS232, RS423, RS422, and RS485 that deal with data communications. EIA standards where previously marked with the prefix "RS" to indicate the recommended standard. Presently, the standards are now generally indicated as "EIA" standards to identify the standards organization.


Electronic data communications will generally fall into two broad categories: single-ended and differential. RS232 (single-ended) was introduced in 1962. RS232 has remained widely used, especially with CNC control builders. The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50' @ the maximum data rate). This 50' limitation can usually be exceeded to distances of 200' or more by using low capacitance cable and keeping the data rates down to 9600 baud and lower.


RTS/CTS Hardware handshaking - uses additional wires to tell a sending device when to stop or start sending data. DTR and RTS refer to these Hardware handshaking lines. You can select whether you need to use DTR or RTS individually or use both lines for hardware handshaking. See also Xon/Xoff.


TCP/IP, Transport Control Protocol / Internet Protocol - TCP and IP are communications protocols, that is, structured languages in which data is communicated between one process and another, and between one network and another. TCP/IP is implemented in a multi-level layered structure.

TCP/IP is the 'glue' that ties together the many heterogeneous networks that make up the Internet.


Stop bits - In data communication, one or two bits used to mark the end of a byte (or character). At least one stop bit is always sent.