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Serial and UART Tutorial - Serial and UART Tutorial Frank...

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Serial and UART Tutorial Frank Durda < [email protected] > $FreeBSD: doc/en_US.ISO8859-1/articles/serial-uart/article.sgml,v 1.14 2010/07/31 11:06:18 pgj Exp $ FreeBSD is a registered trademark of the FreeBSD Foundation. Microsoft, IntelliMouse, MS-DOS, Outlook, Windows, Windows Media and Windows NT are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this document, and the FreeBSD Project was aware of the trademark claim, the designations have been followed by the “™” or the “®” symbol. This article talks about using serial hardware with FreeBSD. [ Split HTML / Single HTML ] Table of Contents 1 The UART: What it is and how it works 2 Configuring the sio driver 3 Configuring the cy driver 4 Configuring the si driver 1 The UART: What it is and how it works Copyright © 1996 Frank Durda IV < [email protected] > , All Rights Reserved. 13 January 1996. The Universal Asynchronous Receiver/Transmitter (UART) controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re- assembles the bits into complete bytes. Serial transmission is commonly used with modems and for non-networked communication between computers, terminals and other devices. There are two primary forms of serial transmission: Synchronous and Asynchronous. Depending on the modes that are supported by the hardware, the name of the communication sub-system will usually include a A if it supports Asynchronous communications, and a S if it supports Synchronous communications. Both forms are described below. Some common acronyms are: UART Universal Asynchronous Receiver/Transmitter USART Universal Synchronous-Asynchronous Receiver/Transmitter
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1.1 Synchronous Serial Transmission Synchronous serial transmission requires that the sender and receiver share a clock with one another, or that the sender provide a strobe or other timing signal so that the receiver knows when to “read” the next bit of the data. In most forms of serial Synchronous communication, if there is no data available at a given instant to transmit, a fill character must be sent instead so that data is always being transmitted. Synchronous communication is usually more efficient because only data bits are transmitted between sender and receiver, and synchronous communication can be more costly if extra wiring and circuits are required to share a clock signal between the sender and receiver. A form of Synchronous transmission is used with printers and fixed disk devices in that the data is sent on one set of wires while a clock or strobe is sent on a different wire. Printers and fixed disk devices are not normally serial devices because most fixed disk interface standards send an
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