A Serial Port Transmits Data Information' title='A Serial Port Transmits Data Information' />How it works and what it does. USB is a system for connecting a wide range of peripherals to a computer, including pointing devices, displays, and data storage and communications products. Although not a relatively new development in personal computing, it has only recently gained popularity due to increasing software support. This document discusses what the USB system does and how it is done. The technical detail covers the systems logical structure, rather than the electrical or software characteristics. About this note This was originally a first year uni assignment, so it is limited in depth and the content is rather dated. Things have changed a lot since then e. USB2, and now 3. Im working on a program which transmits data through serial port. I ended up making this code. It works good when run for the 1st time, afterwords some strange. RS232 Tutorial on Data Interface and cables selection. Serial Data Communication by U. S. Converters LLC How to make a RS232 to RS485 Port Check Serial Accessories Serial Port Cards RS232 to RS485 RS422 Converters. USB, short for Universal Serial Bus, is an industry standard that defines cables, connectors and communications protocols for connection, communication, and power. However, it should still serve as a useful background or introductory note. Where new technical terms are introduced and defined in the text, they are printed in italics like this. Document Contents. Background Why Replace Existing Technologies with USB How the USB system is arranged How Data Gets to the Right Places Types of Data Transfers Low Speed Devices How Data is Sent across the USB Examples of Data Transactions The Role of the Hub The Role of Devices In Conclusion Appendices. Types of Packets. Cyclic Redundancy Checks. References list. 1. Background Why Replace Existing Technologies with USB Traditionally, computer hardware such as printers and mice were plugged into sockets on the back panel of a PC, with each connector being fairly specialised in its applications. For example, mice use one that is dedicated to transmitting serial data, while printers usually use a parallel data cable, and monitors have their own special plug. This system was quite suitable when it was implemented and has been used for many years. However, recent technological developments have created problems for many users of PCs with this system. Today there is a huge range of peripheral equipment including scanners, digital cameras, specialised pointing devices, high speed modems, all of which need their own connection to the PC. While the above mentioned parallel and serial sockets can indeed be used by many different devices, they cannot be shared by more than one device at once, and so we can quickly run out of space to attach this new equipment. Then why not just add more places to plug things into This is quite possible, and has previously been the solution in many cases by installing more sockets, and even connecting devices internally to bypass the need for these plugs altogether. However, there is a practical limit to how much this can be done. To examine why, we need to investigate the structure of the PC. Each of those back panel sockets is attached to a circuit board a card which, like the internal devices, in turn plugs into a slot on the main circuit board. The computer needs to be able to distinguish which of these cards information is coming from, and similarly each card needs to know when out going data is directed to it. This is done by using special numbers called IRQs Interrupt Request, used for when the card wants to get something done, and IO InputOutput addresses, used for transferring data between the computer and cards. When the card has something for the software to do, it generates a signal on the IRQ line, and communicates with the software via the IO addresses. The IRQs and IO addresses are set in hardware on the card but, while these are usually adjustable, people have often found that when adding new hardware these numbers can clash with existing cards. The result is that neither card functions correctly. Many people find these potential problems rather daunting and this reduces the attractiveness of PCs to the market. An innovation known as Plug and Play aims to sort out the problem of clashing numbers, but there are still only a finite amount of these numbers available, with some being reserved for certain purposes. As well as all of the technical problems, where are other nuisances such as excessive cabling, the fact that you cannot disconnect devices while the computer is on without risking damaging something, and the different types of plugs required for different types of computers such as the Apple Macintosh. Even in the absence of problems, that back of a computer can be a daunting place for some, who often fear damaging something. This is where USB aims to simplify things by extending the trend of user friendliness to the hardware level. To the average computer user, it is a system where you can simply plug a device into any available socket and that device will instantly be available for use by the computer. Up to 1. 27 devices can be connected, and since it is a high speed system supporting up to 1. Megabits per second, it can accommodate the needs of a wide variety. Other advantages include the ability to safely disconnect and reconnect items without switching off the computer, and the ability to use a USB device on any computer supporting the USB system. How the USB System is Arranged. The Universal Serial Bus is a network of attachments connected to the host computer. These attachments come in two types known as Functions and Hubs. Functions are the peripherals such as mice, printers, etc. Hubs basically act like a double adapter does on a power point, converting one socket, called a port, into multiple ports. Hubs and functions are collectively called devices. As far as the functions are concerned, hubs are furthermore like double adapters because although the entire system is physically in the star topology seen in Figure 1a, logically the system acts like a bus topology. This means that signals appear to travel along a single set of wiring, called the bus, to the host and is accessible by all functions, as illustrated in Figure 1b. However, the host does keep track of the physical arrangements so that if a hub becomes disconnected, it is aware that all hubs and functions attached to it will consequently be disconnected too. The host has a hub embedded in it called the root hub, and in practical implementations hubs are usually combined with one or more functions, such as keyboards or monitors. These are called compound devices and act like a hub with the functions permanently connected, along with any additional ports. Hubs may be connected to other hubs in a tiered arrangement, but the bus topology still applies. How Does Data Get to the Right PlacesEven with this type of arrangement, we still have the same problem as with the traditional PC layout. Each function has to know when a piece of data is meant for it, and the host needs to know where signals are coming from, so numbers are assigned to each component on the USB. However, rather than each using a fixed IRQ and IO address, the USB system takes a different approach. When a device is attached to the USB system, it gets assigned a number called its address. The address is uniquely used by that device while it is connected and, unlike the traditional system, this number is likely to be different to the address given to that device the last time it was used. Each device also contains a number of endpoints, which are a collection of sources and destinations for communications between the host and the device. Endpoints operate in simplex mode, meaning that they are either an input or output, but not both. Accounting Software Developers In Pakistan Face. For example, a simplistic model of a keyboard figure 2 could have a keypad as output endpoint number 1, and the LED key lock display as receiving endpoint 1. All USB devices have one of each of their 1.