barcode reader project in asp.net Bit 0 Bit 1 Start Bit Bit 0 Bit 3 Bit 4 Parity Stop Bit Bit in Software

Generator QR-Code in Software Bit 0 Bit 1 Start Bit Bit 0 Bit 3 Bit 4 Parity Stop Bit Bit

Bit 0 Bit 1 Start Bit Bit 0 Bit 3 Bit 4 Parity Stop Bit Bit
QR Code 2d Barcode Reader In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Painting QR-Code In None
Using Barcode creation for Software Control to generate, create Quick Response Code image in Software applications.
Data
Reading QR Code ISO/IEC18004 In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
QR Code ISO/IEC18004 Drawer In C#.NET
Using Barcode creation for Visual Studio .NET Control to generate, create Quick Response Code image in .NET framework applications.
Figure 1.23 Data bits with a constant period can be sent together with a leading start bit and stop bit.
QR Code ISO/IEC18004 Maker In .NET
Using Barcode encoder for ASP.NET Control to generate, create Denso QR Bar Code image in ASP.NET applications.
Denso QR Bar Code Generation In VS .NET
Using Barcode creation for .NET framework Control to generate, create Denso QR Bar Code image in Visual Studio .NET applications.
MICROCONTROLLER COMMUNICATION
Encoding Quick Response Code In VB.NET
Using Barcode creation for .NET Control to generate, create QR-Code image in VS .NET applications.
Data Matrix ECC200 Creation In None
Using Barcode generator for Software Control to generate, create Data Matrix 2d barcode image in Software applications.
Bit 0
Make Barcode In None
Using Barcode encoder for Software Control to generate, create bar code image in Software applications.
Encode Code 39 Extended In None
Using Barcode creation for Software Control to generate, create USS Code 39 image in Software applications.
Bit 1
Bar Code Generator In None
Using Barcode drawer for Software Control to generate, create bar code image in Software applications.
Create EAN 13 In None
Using Barcode generator for Software Control to generate, create EAN13 image in Software applications.
Bit 2
ITF Generation In None
Using Barcode generation for Software Control to generate, create I-2/5 image in Software applications.
Reading Barcode In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
Bit 3
Printing Barcode In VS .NET
Using Barcode maker for ASP.NET Control to generate, create barcode image in ASP.NET applications.
USS Code 39 Maker In Java
Using Barcode maker for Java Control to generate, create Code39 image in Java applications.
Bit 4
Encoding Bar Code In .NET Framework
Using Barcode printer for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Print UPC A In Java
Using Barcode encoder for Java Control to generate, create UPC A image in Java applications.
Bit 5
Read EAN13 In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Barcode Reader In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Bit 6
Figure 1.24 Transition in the middle of the bit period indicates its value.
simple parity check bit. The stop bit is some dead air in which the receiver can process the incoming byte and the transmitter can prepare the next one. Finally, the NRZ data packet can be used in common bus point-to-point communication when open collector drivers are used. These points may make NRZ sound like it is quite a complex communications methodology, but in reality it is simple to work with. The Manchester data encoding scheme does not use a voltage level to indicate a bit value, but instead uses the direction of the transition of the incoming data line. Like NRZ, Manchester encoding has a constant bit period (Fig. 1.24), but in the middle of the bit (the dashed line) there is always a level change and, depending on the implementation, a low to high could mean a 0 and a high to low could mean a 1. The need to always have a transition can make a stream of Manchester data hard to interpret when you look at it I nd it to be nonintuitive. When moving from one bit value to another, there is no transition at the bit boundaries, and when two bits are the same value, there is a transition at the point between the two. Manchester encoding is often used in networking protocols where the receive synchs to the incoming signal using a phase locked loop and the level transition is used to toggle in a bit value. Though this sounds complex, the changing logic levels are quite easy to implement in hardware and do not require any timing resources on the part of the receiving processor. The last method of providing point-to-point serial communication on a single line is the pulse-coded data format shown in Fig. 1.25, in which data is indicated by the length of time a signal is active. Whereas NRZ bit values are determined as logic levels at a speci c time and Manchester bit values are logic changes at a speci c time, the length of time a pulse-coded signal varies along with the entire data packet the bit is in. This change in packet timing makes pulse-coded data dif cult to design traditional logic circuitry that reads the incoming data, and generally code must be written to read the incoming data. These two attributes make pulse coding of data to be inef cient in transmission
Timing Start Pulses
Synch Pulse
Figure 1.25 The length of time the signal is active (low) indicates the value of the bit.
EMBEDDED MICROCONTROLLERS
and in the amount of resources required to read the data. For these reasons, pulse-coded data is only used for small amounts of information that is occasionally transmitted. A popular application for pulse-coded data is TV remote controls, which are commonly used for controlling robots and other microcontroller applications.
NETWORK COMMUNICATION
It has only been in the past few years that microcontrollers have been considered legitimate network devices. The drop in cost in powerful microcontrollers and network interface chips for both wired and wireless applications has had a lot to do with the boom in MCU-based network applications. When wireless networks are noted, the Bluetooth and ZigBee protocols should also be considered along with WiFi (802.11) as potential network mediums. Similarly, home Ethernet networks allow for the addition of networked sensors and control devices throughout the house; the old joke of the Internetenabled toaster has never been closer to being a reality. When the second edition of this book was written, there were just a few tentative steps toward creating microcontrollerbased network devices, but in this edition more space will be devoted to showing you how to create networked applications using the PIC MCU. Understanding how a network is laid out and wired will tell you a lot about the various applications that run on it and their characteristics. Rather than use the term layout, computer scientists use the term topology to describe how a network is organized and how different devices (usually referred to as nodes ) are wired to each other. As a simple rule, the more connections nodes have with other nodes within the network, the higher performance (and higher reliability) the network will be. As will be shown, multiple networks of different types can be connected together using nodes known as bridges, which have network interfaces for the different network types. In fact, the Internet is really just a collection of networks that have been networked together at different points. The network topologies shown in this section are really for your edi cation and to familiarize you with some of the terms that will be presented later in the book when networking is discussed. Fully understanding the characteristics of network topologies is really in the realm of computer scientists who are designing networks for speci c applications. Fig. 1.26 shows the prototypical network, the bus or single media network in which a single connection is used to link all the nodes in the network. While bus is the more commonly accepted term, I prefer single media because it s more descriptive and avoids confusion with point-to-point communication using a bus. I also prefer to visualize it using the diagram at the bottom of Fig. 1.26, which looks like a blob (the communications medium) with nodes sprinkled within it. If you visualize the blob of the single media network as air and the connection between the nodes as radio waves, you can see that there can only be one node transmitting at any given time. If you have a WiFi network at home, you should appreciate this model because only one computer can transmit at any time or the messages collide and become garbled. Part of the single media network hardware must be a receiver that monitors the outgoing messages to ensure that messages do not collide. If they do, the transmitter will wait a random amount of time before retrying to send the message. When the nodes are not transmitting, the network
Copyright © OnBarcode.com . All rights reserved.