DNC Glossary

  GLOSSARY OF DNC TERMS

Click on the first letter of the word or term you want to look up.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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A

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Anonymous FTP - Is a means by which archive File Transfer Protocol sites allow general access to their archives of information. These sites create a special account called "anonymous". User "anonymous" has limited access rights to the archive host, as well as some operating restrictions. In fact, the only operations allowed are logging in using FTP, listing the contents of a limited set of directories, and retrieving files. Some sites limit the contents of a directory listing an anonymous user can see as well. Note that "anonymous" users are not usually allowed to transfer files TO the archive site, but can only retrieve files from such a site. See also FTP

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Baud Rate - The transmission speed of data through an asynchronous channel. Often confused with BPS (bits per second), baud rate actually refers to the number of signals per second. Because each signal can represent more than one bit of data, the number of bits per second is usually higher than the baud rate. For example, 2400 bps is typically sent at a rate of 600 baud.

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

There are basically two kinds of computer files, binary and ASCII (also called text-only) files. Computer programs, graphic files and word processor documents are all examples of binary files. These files contain special formatting and computer codes. ASCII files are plain text files that can be read by virtually any word processor.

BTR Stands for Behind-Tape-Reader interface. It is a device that provides older machine tools, that were not equipped originally with a capability to communicate directly with a computer, with a means to communicate. BTR interfaces have the following:

See AMI Advanced Machine Interface - ADR's BTR

BPS - Stands for bits per second (Bits Per Second). This represents the number of data bits that a device such as your modem can transfer within a second. This term is often confused with baud rate.

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

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CAD - Acronym for Computer-Aided-Design. This is used to describe the process of using a computer to first design a part (CAD) and then a computer to develop the NC programs to machine (CAM) the part. CAM Computer-Aided-Manufacturing.

Category 3 -Network cable with performance for vice and data transmission up to 16 MHz or 10 Mbps, such as 10BASE-T.

Category 4 -Network cable with performance for vice and data transmission up to 20 MHz or 16 Mbps, such as 10BASE-T.

Category 5 -Network cable with performance for vice and data transmission up to 100 MHz or 100 Mbps, such as 100BASE-T (twisted pair Ethernet).

CIM - Acronym for Computer-Integrated-Manufacturing is a high technology approach to more efficient manufacturing throughout the entire manufacturing process.

CNC - Computerized Numerical Control Refers to machine tools that have a computer and memory to control their operation.  Most all non manual machine tools sold today will be CNC.  see also NC

COM port - Short for a serial communication port. Most DNC software communicate 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.

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Data bits - A group of bits (1's and 0's) that represent a single character or 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.

DDE - An abbreviation of Dynamic Data Exchange. DDE lets two or more programs that support DDE exchange information and commands while they are running.

DNC - Acronym that can mean Distributed Numerical Control or Direct Numerical Control depending upon the application. In the beginning DNC stood for Direct Numerical Control. A computer provided machine instructions for a NC milling machine that were transmitted over telephone lines. Later the term DNC evolved to mean a system where a group of CNC machines are linked to a central computer. Or conversely a combination of computers are each linked to one or more CNC machines and the computers are linked together by way of a local area network. Distributed Numerical Control where by NC programs are sent (distributed) to the memory of a CNC machine. The program is then run from the CNC memory.

Download - To receive one or more files from a remote computer system, such as a computer sending an NC program to a CNC machine. This can also be files received by a computer from a remote computer system, such as another PC or an online service or the internet.

 

E

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EIA - Format is an older data format used by many older machine tools, teletypes etc. it uses the 7 bit data size, with the eight bit used for error checking. The parity is normally ODD under the ISO format. When EIA format is selected, the information is run through conversion tables to change it to standard ASCII before being saved to disk. On output your ASCII files are converted to EIA format before being transmitted.

F

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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.

FTP - Refers to the File Transfer Protocol, one of the protocols within the TCP/IP protocol group used on the Internet. The FTP Protocol makes it possible to transfer files from one computer (or host) on the Internet to another. A very common use of is to use the FTP program to transfer files from one host to another. FTP is also used frequently to upload files up to a web host for use on the Internet. In manufacturing, FTP is starting to be as a protocol for DNC file transfers. See also Anonymous FTP.

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H

Handshaking - Is the way in which 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.

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I

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ISO - Format is the most widely used data format for NC machines. it uses the 7 bit data size, with the eight bit used for error checking. The parity is normally EVEN under the ISO format. This also called even parity ASCII.

I/O address - An abbreviation for input/output address. Your fax modem uses an I/O address, which is a reserved space in your computer's input/output address space.

IP address - is used by TCP/IP (the Internet) to route data between computers. Each computer and machine has a 32 bit IP address, which can be related to a simple name such as the name of this website. IP addressing allows packets of information to get to their destinations because every network device on the Internet has a unique, numeric address. These numbers are called IP addresses. An IP address usually looks something like this "243.255.255.12" See TCP/IP

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Jumper - A small plug or switch that lets you customize a circuit board. For example, most internal modems let you change their COM port by changing a jumper switch.

K

Kermit - is a file transfer protocol first developed at Columbia University in New York City in 1981 for the specific purpose of transferring text and binary files without errors between diverse types of computers over potentially hostile communication links. It is sometimes used in CNC communications.

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M

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Modem - An abbreviation for MOdulator/DEModulator, a device that lets computers exchange information over a standard telephone line. Computers process information in 1's and 0's called bits. A modem takes these bits from a computer and modulates them into high and low signals that a telephone line can carry. The receiving modem then demodulates them back into 1's and 0's, which the receiving computer can understand.

MRP - Manufacturing Resource Planning - An automated software system for handling information directly related to manufacturing, including bills of material, inventory and orders from purchasing.

MRP II - Manufacturing Resource Planning II - An expanded version of MRP that includes an enhanced capability for planning and scheduling the use of all manufacturing resources. See also CRP

 

N

NC - Numerical Conrol The operation of a machine by a series of coded instruction's that consist of numbers and letters of the alphabet and other symbols.  These are translated into pulses of electrical current or other output signals that active motors and other device to run the machine. On early NC machines these signals was often delivered to the machines by using punched tape.  Also, the term NC machine refers to machine tools that do not have a computer and memory installed.  see also CNC

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OCR - An abbreviation of Optical Character Recognition, a process of recognizing the graphical representations of text and translating it into a format that a word processor can read.

Online - In data communications, a successful connection with a remote computer.

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Padding - Some fax machines and modems expect a certain amount of data for each fax scan line. If a scan line has little or no data, Transmit Fax can, if required, automatically insert "filler" or padding characters (0's) so each scan line is a predefined length. Generally, the newer fax machines and modems do not require padding.

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 add up to an even number, and None, in which a parity bit is not added.

Protocol - A set of rules and conventions to ensure that two modems exchange data without errors. Both sides must use the same protocol. Protocols exist at several levels in a telecommunication connection. There are hardware telephone protocols. There are protocols between the end points in communicating programs within the same computer or at different locations. Both end points must recognize and observe the protocol. Xmodem, Zmodem, Kermit

There is a comprehensive Protocol Directory. http://www.protocols.com/pbook/index.htm

PUNCH- CNC output device - used in CNC machines to output programs to perforated tape. Units can be parallel to tape punch or serial output.

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R

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RS244 - see EIA an early character set used in numerical control machines

RS358 - A newer character set used by CNC machines, also know as ISO.  Identifying feature is that all characters have even parity.

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.

RS423 is another single ended specification with enhanced operation over RS232; however, it has not been widely used.

When communicating at high data rates, or over long distances, single-ended methods such as RS232 are often inadequate. Differential data transmission (balanced differential signal) offers superior performance. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. RS422 (differential) was designed for greater distances and higher Baud rates than RS232. In its simplest form, a pair of converters from RS232 to RS422 (and back again) can be used. Data rates of up to 100K bits / second and distances up to 4000 Ft. can be accommodated with RS422. RS232 to RS422 converters are commonly used with DNC systems to extend the distance between the DNC computer and the machine tool. Some CNC machine controls also offer RS422 as an alternative to RS232.

RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. RS485 is not commonly found in CNC machine controls as a serial data communications method.

SUMMARY OF "RS"

SPECIFICATIONS
RS232
RS423
RS422
RS485
Maximum Data Rate 20kb/s 100kb/s 10Mb/s 10Mb/s
Maximum Cable Length 50 Feet 4000 Feet 4000 Feet 4000 Feet
Total Number of Drivers and Receivers on One Line

1 DRIVER & 1 RECEIVER

1 DRIVER & 10 RECEIVERS

1 DRIVER & 10 RECEIVERS

1 DRIVER & 32 RECEIVERS

Mode of Operation SINGLE ENDED SINGLE ENDED DIFFERENTIAL DIFFERENTIAL
Maximum Driver Output Voltage +/-25V +/-6V -0.25V to +6V -7V to +12V

 

RTS/CTS Hardware handshaking - uses additonal 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

 

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Start bit - The startng bit of a byte (or character). In data communications, every byte has a starting bit.

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.

T

T-1 Line - A leased-line connection capable of carrying data at 1,544,000 bits-per-second.

T-3 Line - A leased-line connection capable of carrying data at 44,736,000 bits-per-second.

TCP - TRANSMISSION CONTROL PROTOCOL

Telnet - A program that is used to login from one Internet site to another. The telnet program gets you to the login: prompt of another host.

Terminal - A device or software program that allows you to send commands to a computer somewhere else. This can be only a keyboard and a display screen. In DNC applications this is a screen in software that emulates a physical terminal and allows you to type commands to a computer or CNC machine. With a terminal you can see all the characters that are being sent and received. This is very useful in establishing initial communications with CNC machines.

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Terminal emulation - A technique of making a computer act as if it were a particular type of terminal, such as ANSI or VT100. This is useful in see the actual data that is being sent and received during serial communications..

TCP/IP - is want makes the Internet run. The term TCP/IP, which stands for Transmission Control Protocol/Internet Protocol, actually refers to a whole family of protocols, of which TCP and IP are just two. see also IP Address

U

UART - The acronym for Universal Asynchronous Receiver/Transmitter. A UART is a chip that processes the data that goes through your modem. If you are using fax/voice modem, you should use a 16550 or 16550A UART to help ensure clear voice messages.

Upload - To send one or more files from your computer's disk storage to a remote computer. In DNC this usually means from the CNC machine's control back to the DNC computer. This can also mean from your computer's disk to a remote computer, such as another PC or an online service or the internet.

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V

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W

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X

Xmodem - is an error-correcting protocol for modems that was created in 1978 by Ward Christensen. It has become a standard. Modems that agree on using the Xmodem protocol send data in 128-byte blocks. If a block is received successfully, a positive (ACK) acknowledgement is returned. If an error is detected, a negative (NAK) acknowledgement is returned and the block is resent. Xmodem uses the checksum method of error checking.

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Xon/Xoff Flow Control - Uses the Xon/Xoff characters to tell the sending device to start and stop sending information. When a receiving device's buffer is nearly full, it will transmit an Xoff character to the sending device. The sending device will stop sending characters until the receiving device sends an Xon character. Xon is normally ASCII value decimal 17 and Xoff is normally ASCII decimal value 19. See also RTS/CTS

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Z

Zmodem - is an error-correcting protocol for modems. Modems that agree on using the Zmodem protocol send data in 512-byte blocks. If a block arrives and an error is detected, a "NAK" (negative acknowledgement) is returned and the block is resent.

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