barcode project in vb.net First Things First in Software

Draw Code 3 of 9 in Software First Things First

First Things First
Recognizing Code 3/9 In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Make Code 3/9 In None
Using Barcode generator for Software Control to generate, create Code 3/9 image in Software applications.
Figure 1-1 Voltage representations of data
Code39 Recognizer In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
Generating Code 39 In C#
Using Barcode drawer for .NET Control to generate, create Code 3 of 9 image in Visual Studio .NET applications.
1
Print Code39 In VS .NET
Using Barcode generation for ASP.NET Control to generate, create USS Code 39 image in ASP.NET applications.
Code-39 Creation In Visual Studio .NET
Using Barcode encoder for .NET Control to generate, create Code 39 image in .NET applications.
as a 300-volt pulse, and the printer expects a 3-volt pulse, the two devices will have a brief (but exciting!) conversation, the ultimate result of which will be the release of a small puff of silicon smoke from the printer. Now they have to decide on a standard that they will use for actually originating and terminating the data that they will exchange. They are connected by a cable (Figure 1-2) that has nine pins on one end and nine jacks on the other. Logically, the internal wiring of the cable would look like Figure 1-3. However, when we stop to think about it, this one-to-one correspondence of pin-to-socket will not work. If the PC transmits on pin 2, which in our example is identified as the send data lead, it will arrive at the printer on pin 2 the send data lead. This would be analogous to holding two telephone handsets together so that two communicating parties can talk. It won t work without a great deal of hollering, since the handsets are oriented microphone-to-microphone and speaker-tospeaker! Instead, some agreement has to be forged to ensure that the traffic placed on the send data lead somehow arrives on the receive data lead, and vice versa. Similarly, the other leads must be able to convey information to the other end so that normal transmission can be started and stopped. For example, if the printer is ready to receive the print file, it might put voltage on the data terminal ready (DTR) lead, which signals to the PC that it is ready to receive traffic. The PC might respond by setting its own DTR lead high, as a form of acknowledgement, and then transmitting the file that is to be printed. The printer will keep its DTR lead high until it wants the PC to stop sending. For example, if the printer senses that it is running out of buffer space because the PC is transmitting faster than the slower printer can print, it will drop the DTR lead, causing the PC to temporarily halt its transmission of the print file. As soon as the printer is ready to receive again, it sets the DTR lead high, and printing resumes. As long as both the transmitter and the receiver abide by this standard set of rules, data communications will work properly. This process of swapping the data on the various leads of a cable, incidentally, is done by the modem or by a null modem cable
Code 3 Of 9 Generation In VB.NET
Using Barcode encoder for VS .NET Control to generate, create USS Code 39 image in VS .NET applications.
ANSI/AIM Code 39 Printer In None
Using Barcode creation for Software Control to generate, create Code 3/9 image in Software applications.
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
UCC - 12 Drawer In None
Using Barcode generation for Software Control to generate, create EAN128 image in Software applications.
Making Data Matrix ECC200 In None
Using Barcode encoder for Software Control to generate, create DataMatrix image in Software applications.
First Things First
Drawing Barcode In None
Using Barcode drawer for Software Control to generate, create bar code image in Software applications.
Printing Bar Code In None
Using Barcode generation for Software Control to generate, create bar code image in Software applications.
First Things First
Create NW-7 In None
Using Barcode creation for Software Control to generate, create USS Codabar image in Software applications.
Paint UPC-A In None
Using Barcode encoder for Word Control to generate, create UPC Code image in Office Word applications.
Figure 1-2 Pin assignments on a cable connector
Scan Barcode In Visual Studio .NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in VS .NET applications.
Encode Barcode In None
Using Barcode generation for Font Control to generate, create barcode image in Font applications.
Send Data (pin 2)
Barcode Recognizer In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
Paint Bar Code In Objective-C
Using Barcode encoder for iPhone Control to generate, create bar code image in iPhone applications.
Receive Data Request to Send Clear to Send
Painting Bar Code In VB.NET
Using Barcode generator for .NET framework Control to generate, create barcode image in .NET framework applications.
Barcode Recognizer In Visual Basic .NET
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in VS .NET applications.
Ground Carrier Data Set Ready Data Terminal Ready
Figure 1-3 Logical wiring scheme
that makes the communicating devices think they are talking to a modem. The null modem cable is wired so that the send data lead on one end is connected to the receive data lead on the other end, and vice-versa. Similarly, a number of control leads such as the carrier detect lead, the DTR lead, and the data set ready (DSR) lead are wired together so that they give false indications to each other to indicate that they are ready to proceed with a transmission, when in fact no response from the far end modem has been received.
Standards: Where Do They Come From
Physicists, electrical engineers, and computer scientists generally design data communications protocols. For example, the Transmission Control
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
First Things First
1
Protocol (TCP) and the Internet Protocol (IP), discussed in detail later in the book, were written during the heady days of the Internet, back in the 1960s, by such early pioneers as Vinton Cerf and the late John Postel (I want to say, back in the last century, to make them seem like real pioneers!). Standards, on the other hand, are created as the result of a consensus-building process that can take years to complete. By design, standards must meet the requirements of the entire data and telecommunications industry, which is of course global. It makes sense, therefore, that some international body be responsible for overseeing the creation of international standards. One such body is the United Nations (UN). Its 150 member nations work together in an attempt to harmonize whatever differences they have at various levels of interaction, one of which is international telecommunications. The International Telecommunications Union (ITU), a suborganization of the UN, is responsible for not only coordinating the creation of worldwide standards but also publishing them under the auspices of its own suborganizations. These include the Telecommunications Standardization Sector (TSS, sometimes called the ITU-T, and formerly called the Consultative Committee on International Telegraphy and Telephony, or the CCITT), the Telecommunications Development Sector (TDS), and the Radio Communication Sector (RCS, formerly the Consultative Committee on International Radio, or the CCIR). The organizational structure is shown in Figure 1-4. Of course, the UN and its suborganizations cannot perform this task alone, nor should they. Instead, they rely upon the input of hundreds of industry-specific organizations as well as local, regional, national, and
Copyright © OnBarcode.com . All rights reserved.