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REDES INDUSTRIALES. ING. ALFONSO PEREZ GARCIA. INSTITUTO TECNLOGICO DE SAN LUIS POTOSI. ING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI
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REDES INDUSTRIALES. ING. ALFONSO PEREZ GARCIA. INSTITUTO TECNLOGICO DE SAN LUIS POTOSI.

ING. ALFONSO PEREZ GARCIA

INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

INDICE

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INDICE.

PROGRAMA Prcticas. BIBLIOGRAFIA. UNIDAD 1 MODELO OSI1.1 El modelo OSI. Modelo OSIHistoria Modelo de referencia OSI Capa Fsica (Capa 1) Codificacin de la seal Topologa y medios compartidos Equipos adicionales Capa de enlace de datos (Capa 2) Capa de red (Capa 3) Capa de transporte (Capa 4) Capa de sesin (Capa 5) Capa de presentacin (Capa 6) Capa de aplicacin (Capa 7) Unidades de datos Transmisin de los datos Formato de los datos Operaciones sobre los datos Bloqueo y desbloqueo Concatenacin y separacin

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Vase tambin Enlaces externos 1.2 Su relacin con las redes industriales Red industrialINTRODUCCIN LA TECNOLOGA DE BUSES DE CAMPO ALGUNOS TIPOS DE BUS CLASIFICACION DE LAS REDES INDUSTRIALES. COMPONENTES DE LAS REDES INDUSTRIALES. TOPOLOGIA DE REDES INDUSTRIALES BENEFICIOS DE UNA RED INDUSTRIAL REDES INDUSTRIALES CON PLC SOLUCIONES CON ETHERNET CONCLUSION

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UNIDAD 2 LAYERS FISICOS2.1 Los estandares RS232, IEEE-488 y RS485 RS-232Scope of the standard History Limitations of the standard Role in modern personal computers Standard details Conventions RTS/CTS handshaking 3-wire and 5-wire RS-232 ING. ALFONSO PEREZ GARCIA

Enlaces externos

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INDICE Seldom used features Signal rate selection Loopback testing Timing signals Secondary channel Related standards

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See also References External linksEIA-485 Waveform example References See also External links

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Interface Converter RS232 to RS485 cable pinout IEEE-488History Applications Signals Connectors

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See also References External links 2.2 El lazo de corriente 4-20 Ma y HART HART ProtocolAnalog/digital mode Multidrop mode Packet Structure

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UNIDAD 3 FIELDBUS

External links

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3.1 INTRODUCCION. 59 ANALISIS DEL ESTADO DEL ARTE DE LOS BUSES DE CAMPO APLICADOS AL CONTROL DE PROCESOS INDUSTRIALES 59RESUMEN 1. INTRODUCCIN 2. VENTAJAS DE LOS BUSES DE CAMPO 3. BUSES DE CAMPO EXISTENTES 4. ALGUNOS BUSES ESTANDARIZADOS 5. LA GUERRA DE LOS BUSES. 6. CONCLUSIONES BIBLIOGRAFIA 59 59 60 62 63 70 71 71

UNIDAD 4 BITBUS

3.2 ESPECIFICACION. 3.3 APLICACIONES. 4.1 INTRODUCCION. Cableado y terminaciones Conectores Estructura Tipos de nodos Modos de sincronizacin Codificacin Trama del mensaje

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INDICE Flag Direccin esclavo Control Informacin CRC

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Trama del campo de informacinLongitud de informacin Tipo de mensaje (MT) Fuente de la orden (SE) Destino de la orden (DE) Pista (TR) 4 bits reservados Direccin esclavo Codificacin de tareas Tareas usuario/Errores Datos

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Registros de estado y contadores de secuencia Bibliografa

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What is BITBUS?What is the History of BITBUS? What are the Features of the iDCX 51 real time operating system? Can I still get BITBUS software? Can I still get BITBUS hardware? Can I still get BITBUS documentation?

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BITBUS Basics UNIDAD 5 ASi

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4.2 ESPECIFICACION. 4.3 APLICACIONES. 5.1 INTRODUCCION. AS-interface

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AS-Interface

Caractersticas principales Enlaces externos

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UNIDAD 6 CAN

External links 5.2 ESPECIFICACION. 5.3 APLICACIONES. 6.1 INTRODUCCION. Controller Area NetworkOrigins Applications CAN Network Testing Technology

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UNIDAD 7 DEVICENET7.1 INTRODUCCION DeviceNetHistory ING. ALFONSO PEREZ GARCIA

See also References External links 6.2 ESPECIFICACION. 6.3 APLICACIONES.

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INDICE Technical Snapshot Architecture Conformance Test Sources

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UNIDAD 8 PROFIBUS8.1 INTRODUCCION. Profibus Vase tambin Enlaces externos ProfibusFrom Wikipedia, the free encyclopedia Retrieved from "http://en.wikipedia.org/wiki/Profibus" Origin Use Technology Standardization Organization

7.2 ESPECIFICACION. 7.3 APLICACIONES.

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References External links 8.2 ESPECIFICACION. 8.3 APLICACIONES.

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UNIDAD 9 ETHERNET9.1 INTRODUCCION. PROFINETTechnology PROFINET CBA PROFINET IO Organization Weblinks

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9.2 ESPECIFICACION. 9.3 APLICACIONES.

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PROGRAMAS.E.P. DIRECCIN GENERAL DE INSTITUTOS TECNOLGICOS S.E.l.T 1. IDENTIFICACION DEL PROGRAMA DESARROLLADO POR UNIDADES DE APRENDIZAJE. NOMBRE DE LA ASIGNATURA: NIVEL: CARRERA: CLAVE: REDES INDUSTRIALES (3-2-8). LICENCIATURA. INGENIERIA ELECTRONICA. ECM 0705

NUMER O 1 2

TEMA MODELO OSI LAYERS FISICOS

SUBTEMAS: 1.1 El modelo OSI. 1.2 Su relacin con las redes industriales 2.1 Los estandares RS232, RS488 y RS485 2.2 El lazo de corriente 420 Ma y HART 3.1 INTRODUCCION. 3.2 ESPECIFICACION. 4.1 INTRODUCCION. 4.2 ESPECIFICACION. 5.1 INTRODUCCION. 5.2 ESPECIFICACION. 6.1 INTRODUCCION. 6.2 ESPECIFICACION. 7.1 INTRODUCCION 7.2 ESPECIFICACION. 8.1 INTRODUCCION. 8.2 ESPECIFICACION. 9.1 INTRODUCCION. 9.2 ESPECIFICACION.

DURACIO EVAL. N 1 100% SEMANAS EE 1 100% SEMANAS EE

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FIELDBUS BITBUS ASi CAN DEVICENET PROFIBUS ETHERNET

3.3 APLICACIONES. 4.3 APLICACIONES. 5.3 APLICACIONES. 6.3 APLICACIONES. 7.3 APLICACIONES. 8.3 APLICACIONES. 9.3 APLICACIONES.

2 SEMANAS 2 SEMANA 2 SEMANAS 2 SEMANAS 2 SEMANA 2 SEMANA 2 SEMANA

100% EE 100% EE 100% EE 100% EE 100% EE 100% EE 100% EE

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Prcticas.NUMERO DE PRACTICA. 1 2 3 DESCRIPCION (TEMA). Red simple con protocolo HART Red simple de actuadores y sensores digitales con ASi. Red simple con protocolo Ethernet. 2 5 9 UNIDAD.

BIBLIOGRAFIA.AUTOR

1 Steve Mackay, Edwin Wright, Deon Reynders, John Park 2 Franco Davoli, Sergio Palazzo, Distributed Cooperative Laboratories: Networking, Sandro Zappatore Instrumentation, and Measurements (Signals and Communication Technology) 3 N. P. Mahalik Fieldbus Technology: Industrial Network Standards for Real-Time Distributed Control (Hardcover) NOMBRE HOW STUFF WORKS ESNIPS PAGINA PROFE FAIRCHILD SEMICONDUCTORS B&B ELECTRONICS. DIRECCION WWW.HOWSTUFFWORKS.COM DEL WWW.ESNIPS.COM/WEB/REDESINDUSTRIA LES WWW.FAIRCHILDSEMI.COM WWW.BB-ELEC.COM WWW.HARTCOMM.ORG WWW.FIELBUS.ORG

TITULO Practical Industrial Data Networks: Design, Installation and Troubleshooting (IDC Technology (Paperback)) (Paperback)

EDITORIAL

Newnes (July 2003) Springer; 1 edition (April 5, 2006) Springer; 1 edition (October 19, 2005) TEMAS

TODOS TODOS OPTOACOPLADORES RS232, RS488 Y RS485 HART PROTOCOL FIELDBUS ORGANIZATION

ING. ALFONSO PEREZ GARCIA

INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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ING. ALFONSO PEREZ GARCIA

INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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UNIDAD 1 MODELO OSI1.1 El modelo OSI. Modelo OSIDe Wikipedia, la enciclopedia libre

El modelo de referencia de Interconexin de Sistemas Abiertos (OSI, Open System Interconnection) lanzado en 1984 fue el modelo de red descriptivo creado por ISO.Historia

A principios de la dcada de 1980 el desarrollo de redes sucedi con desorden en muchos sentidos. Se produjo un enorme crecimiento en la cantidad y el tamao de las redes. A medida que las empresas tomaron conciencia de las ventajas de usar tecnologa de networking, las redes se agregaban o expandan a casi la misma velocidad a la que se introducan las nuevas tecnologas de red. Para mediados de la dcada de 1980, estas empresas comenzaron a sufrir las consecuencias de la rpida expansin. De la misma forma en que las personas que no hablan un mismo idioma tienen dificultades para comunicarse, las redes que utilizaban diferentes especificaciones e implementaciones tenan dificultades para intercambiar informacin. El mismo problema surga con las empresas que desarrollaban tecnologas de networking privadas o propietarias. "Propietario" significa que una sola empresa o un pequeo grupo de empresas controla todo uso de la tecnologa. Las tecnologas de networking que respetaban reglas propietarias en forma estricta no podan comunicarse con tecnologas que usaban reglas propietarias diferentes. Para enfrentar el problema de incompatibilidad de redes, la Organizacin Internacional para la Estandarizacin (ISO) investig modelos de networking como la red de Digital Equipment Corporation (DECnet), la Arquitectura de Sistemas de Red (SNA) y TCP/IP a fin de encontrar un conjunto de reglas aplicables de forma general a todas las redes. Con base en esta investigacin, la ISO desarroll un modelo de red que ayuda a los fabricantes a crear redes que sean compatibles con otras redes.

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Siguiendo el esquema de este modelo se crearon numerosos protocolos, por ejemplo X.25, que durante muchos aos ocuparon el centro de la escena de las comunicaciones informticas. El advenimiento de protocolos ms flexibles donde las capas no estn tan demarcadas y la correspondencia con los niveles no era tan clara puso a este esquema en un segundo plano. Sin embargo sigue siendo muy usado en la enseanza como una manera de mostrar como puede estructurarse una "pila" de protocolos de comunicaciones (sin importar su poca correspondencia con la realidad). El modelo en s mismo no puede ser considerado una arquitectura, ya que no especifica el protocolo que debe ser usado en cada capa, sino que suele hablarse de modelo de referencia. Este modelo est dividido en siete capas:Capa Fsica (Capa 1)

Artculo principal: Nivel fsico

La Capa Fsica del modelo de referencia OSI es la que se encarga de las conexiones fsicas de la computadora hacia la red, tanto en lo que se refiere al medio fsico (medios guiados: cable coaxial, cable de par trenzado, fibra ptica y otros tipos de cables; medios no guiados: radio, infrarrojos, microondas, lser y otras redes inalmbricas); caractersticas del medio (p.e. tipo de cable o calidad del mismo; tipo de conectores normalizados o en su caso tipo de antena; etc.) y la forma en la que se transmite la informacin (codificacin de seal, niveles de tensin/intensidad de corriente elctrica, modulacin, tasa binaria, etc.) Es la encargada de transmitir los bits de informacin a travs del medio utilizado para la transmisin. Se ocupa de las propiedades fsicas y caractersticas elctricas de los diversos componentes; de la velocidad de transmisin, si sta es uni o bidireccional (smplex, dplex o full-dplex). Tambin de aspectos mecnicos de las conexiones y terminales, incluyendo la interpretacin de las seales elctricas/electromagnticas. Se encarga de transformar una trama de datos proveniente del nivel de enlace en una seal adecuada al medio fsico utilizado en la transmisin. Estos impulsos pueden ser elctricos (transmisin por cable) o electromagnticos (transmisin sin cables). Estos ltimos, dependiendo de la frecuencia / longitud de onda de la seal pueden ser pticos, de micro-ondas o de radio. Cuando acta en modo recepcin el trabajo es inverso; se encarga de transformar la seal transmitida en tramas de datos binarios que sern entregados al nivel de enlace. Sus principales funciones se pueden resumir como:

Definir el medio o medios fsicos por los que va a viajar la comunicacin: cable de pares trenzados (o no, como en RS232/EIA232), coaxial, guas de onda, aire, fibra ptica.

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Definir las caractersticas materiales (componentes y conectores mecnicos) y elctricas (niveles de tensin) que se van a usar en la transmisin de los datos por los medios fsicos. Definir las caractersticas funcionales de la interfaz (establecimiento, mantenimiento y liberacin del enlace fsico). Transmitir el flujo de bits a travs del medio. Manejar las seales elctricas/electromagnticas Especificar cables, conectores y componentes de interfaz con el medio de transmisin, polos en un enchufe, etc. Garantizar la conexin (aunque no la fiabilidad de sta).

Codificacin de la seal

El nivel fsico recibe una trama binaria que debe convertir a una seal elctrica, electromagntica u otra dependiendo del medio, de tal forma que a pesar de la degradacin que pueda sufrir en el medio de transmisin vuelva a ser interpretable correctamente en el receptor. En el caso ms sencillo el medio es directamente digital, como en el caso de las fibras pticas, dado que por ellas se transmiten pulsos de luz. Cuando el medio no es digital hay que codificar la seal, en los casos ms sencillos la codificacin puede ser por pulsos de tensin (PCM o Pulse Code Modulatin) (por ejemplo 5 V para los "unos" y 0 V para los "ceros"), es lo que se llaman codificacin unipolar RZ. Otros medios se codifican mediante presencia o ausencia de corriente. En general estas codificaciones son muy simples y no usan bien la capacidad de medio. Cuando se quiere sacar ms partido al medio se usan tcnicas de modulacin ms complejas, y suelen ser muy dependientes de las caractersticas del medio concreto. En los casos ms complejos, como suelen ser las comunicaciones inalmbricas, se pueden dar modulaciones muy sofisticadas, este es el caso de los estndares WiFi, con tcnicas de modulacin complejas de espectro ensanchadoTopologa y medios compartidos

Indirectamente, el tipo de conexin que se haga en la capa fsica puede influir en el diseo de la capa de Enlace. Atendiendo al nmero de equipos que comparten un medio hay dos posibilidades: Conexiones punto a punto: que se establecen entre dos equipos y que no admiten ser compartidas por terceros Conexiones multipunto: en la que ms de dos equipos pueden usar el medio. As por ejemplo la fibra ptica no permite fcilmente conexiones multipunto (sin embargo, vase FDDI) y por el contrario las conexiones inalmbricas son inherentemente multipunto (sin embargo, vanse los enlaces infrarrojos). Hay topologas como el anillo, que permiten conectar muchas mquinas a partir de una serie de conexiones punto a punto.Equipos adicionales

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A la hora de disear una red hay equipos adicionales que pueden funcionar a nivel fsico, se trata de los repetidores, en esencia se trata de equipos que amplifican la seal, pudiendo tambin regenerarla. En las redes Ethernet con la opcin de cableado de par trenzado (la ms comn hoy por hoy) se emplean unos equipos de interconexin llamados concentradores (repetidores en las redes 10Base-2) ms conocidos por su nombre en ingls (hubs) que convierten una topologa fsica en estrella en un bus lgico y que actan exclusivamente a nivel fsico, a diferencia de los conmutadores (switches) que actan a nivel de enlace.Capa de enlace de datos (Capa 2)

Artculo principal: Nivel de enlace de datos

Cualquier medio de transmisin debe ser capaz de proporcionar una transmisin sin errores, es decir, un trnsito de datos fiable a travs de un enlace fsico. Debe crear y reconocer los lmites de las tramas, as como resolver los problemas derivados del deterioro, prdida o duplicidad de las tramas. Tambin puede incluir algn mecanismo de regulacin del trfico que evite la saturacin de un receptor que sea ms lento que el emisor. La capa de enlace de datos se ocupa del direccionamiento fsico, de la topologa de la red, del acceso a la red, de la notificacin de errores, de la distribucin ordenada de tramas y del control del flujo. Se hace un direccionamiento de los datos en la red ya sea en la distribucin adecuada desde un emisor a un receptor, la notificacin de errores, de la topologa de la red de cualquier tipo. La tarjeta NIC (Network Interface Card, Tarjeta de Interfaz de Red en espaol o Tarjeta de Red) que se encarga que tengamos conexin, posee una direccin MAC (control de acceso al medio) y la LLC (control de enlace lgico). La PDU de la capa 2 es la trama.Capa de red (Capa 3)

Artculo principal: Nivel de red

El cometido de la capa de red es hacer que los datos lleguen desde el origen al destino, an cuando ambos no estn conectados directamente. Los dispositivos que facilitan tal tarea se denominan en castellano encaminadores, aunque es ms frecuente encontrar el nombre ingls routers y, en ocasiones enrutadores. Adicionalmente la capa de red debe gestionar la congestin de red, que es el fenmeno que se produce cuando una saturacin de un nodo tira abajo toda la red (similar a un atasco en un cruce importante en una ciudad grande). La PDU de la capa 3 es el paquete. Los switch tambin pueden trabajar en esta capa dependiendo de la funcin que se le asigne.Capa de transporte (Capa 4)

Artculo principal: Nivel de transporte

Su funcin bsica es aceptar los datos enviados por las capas superiores, dividirlos en pequeas partes si es necesario, y pasarlos a la capa de red. En el caso del modelo OSI, tambin se asegura que lleguen correctamente al otro ladoING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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de la comunicacin. Otra caracterstica a destacar es que debe aislar a las capas superiores de las distintas posibles implementaciones de tecnologas de red en las capas inferiores, lo que la convierte en el corazn de la comunicacin. En esta capa se proveen servicios de conexin para la capa de sesin que sern utilizados finalmente por los usuarios de la red al enviar y recibir paquetes. Estos servicios estarn asociados al tipo de comunicacin empleada, la cual puede ser diferente segn el requerimiento que se le haga a la capa de transporte. Por ejemplo, la comunicacin puede ser manejada para que los paquetes sean entregados en el orden exacto en que se enviaron, asegurando una comunicacin punto a punto libre de errores, o sin tener en cuenta el orden de envo. Una de las dos modalidades debe establecerse antes de comenzar la comunicacin para que una sesin determinada enve paquetes, y se ser el tipo de servicio brindado por la capa de transporte hasta que la sesin finalice. De la explicacin del funcionamiento de esta capa se desprende que no est tan encadenada a capas inferiores como en el caso de las capas 1 a 3, sino que el servicio a prestar se determina cada vez que una sesin desea establecer una comunicacin. Todo el servicio que presta la capa est gestionado por las cabeceras que agrega al paquete a transmitir. En resumen, podemos definir a la capa de transporte como: Capa encargada de efectuar el transporte de los datos (que se encuentran dentro del paquete) de la mquina origen a la destino, independizndolo del tipo de red fsica que se est utilizando. La PDU de la capa 4 se llama Segmentos.Capa de sesin (Capa 5)

Artculo principal: Nivel de sesin

Esta capa Establece, gestiona y finaliza las conexiones entre usuarios (procesos o aplicaciones) finales. Ofrece varios servicios que son cruciales para la comunicacin, como son: Control de la sesin a establecer entre el emisor y el receptor (quin transmite, quin escucha y seguimiento de sta). Control de la concurrencia (que dos comunicaciones a la misma operacin crtica no se efecten al mismo tiempo). Mantener puntos de verificacin (checkpoints), que sirven para que, ante una interrupcin de transmisin por cualquier causa, la misma se pueda reanudar desde el ltimo punto de verificacin en lugar de repetirla desde el principio. Por lo tanto, el servicio provisto por esta capa es la capacidad de asegurar que, dada una sesin establecida entre dos mquinas, la misma se pueda efectuar para las operaciones definidas de principio a fin, reanudndolas en caso de interrupcin. En muchos casos, los servicios de la capa de sesin son parcialmente, o incluso, totalmente prescindibles. En conclusin esta capa es la que se encarga de mantener el enlace entre los dos computadores que estn trasmitiendo archivos.Capa de presentacin (Capa 6)

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El objetivo de la capa de presentacin es encargarse de la representacin de la informacin, de manera que aunque distintos equipos puedan tener diferentes representaciones internas de caracteres (ASCII, Unicode, EBCDIC), nmeros (littleendian tipo Intel, big-endian tipo Motorola), sonido o imgenes, los datos lleguen de manera reconocible. Esta capa es la primera en trabajar ms el contenido de la comunicacin que cmo se establece la misma. En ella se tratan aspectos tales como la semntica y la sintaxis de los datos transmitidos, ya que distintas computadoras pueden tener diferentes formas de manejarlas. Por lo tanto, podemos resumir definiendo a esta capa como la encargada de manejar las estructuras de datos abstractas y realizar las conversiones de representacin de datos necesarias para la correcta interpretacin de los mismos. Esta capa tambin permite cifrar los datos y comprimirlos. En pocas palabras es un traductorCapa de aplicacin (Capa 7)

Ofrece a las aplicaciones(de usuario o no) la posibilidad de acceder a los servicios de las dems capas y define los protocolos que utilizan las aplicaciones para intercambiar datos, como correo electrnico (POP y SMTP), gestores de bases de datos y servidor de ficheros (FTP). Hay tantos protocolos como aplicaciones distintas y puesto que continuamente se desarrollan nuevas aplicaciones el nmero de protocolos crece sin parar. Cabe aclarar que el usuario normalmente no interacta directamente con el nivel de aplicacin. Suele interactuar con programas que a su vez interactan con el nivel de aplicacin pero ocultando la complejidad subyacente. As por ejemplo un usuario no manda una peticin "HTTP/1.0 GET index.html" para conseguir una pgina en html, ni lee directamente el cdigo html/xml. Entre los protocolos (refirindose a protocolos genricos, no a protocolos de la capa de aplicacin de OSI) ms conocidos destacan: HTTP (HyperText Transfer Protocol) el protocolo bajo la www FTP (File Transfer Protocol) ( FTAM, fuera de TCP/IP) transferencia de ficheros SMTP (Simple Mail Transfer Protocol) (X.400 fuera de tcp/ip) envo y distribucin de correo electrnico POP (Post Office Protocol)/IMAP: reparto de correo al usuario final SSH (Secure SHell) principalmente terminal remoto, aunque en realidad cifra casi cualquier tipo de transmisin. Telnet otro terminal remoto, ha cado en desuso por su inseguridad intrnseca, ya que las claves viajan sin cifrar por la red. Hay otros protocolos de nivel de aplicacin que facilitan el uso y administracin de la red: SNMP (Simple Network Management Protocol) DNS (Domain Name System) Unidades de datos

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INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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El intercambio de informacin entre dos capas OSI consiste en que cada capa en el sistema fuente le agrega informacin de control a los datos, y cada capa en el sistema de destino analiza y remueve la informacin de control de los datos como sigue: Si un ordenador (host A) desea enviar datos a otro (host B), en primer trmino los datos deben empaquetarse a travs de un proceso denominado encapsulamiento, es decir, a medida que los datos se desplazan a travs de las capas del modelo OSI, reciben encabezados, informacin final y otros tipos de informacin.

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N-PDU (Unidad de datos de protocolo) Es la informacin intercambiada entre entidades pares,es decir,dos entidades pertenecientes a la misma capa pero en dos sistemas diferentes, utilizando una conexin(N-1). Esta compuesta por: N-SDU (Unidad de datos del servicio) Son los datos que se necesitan la entidades(N) para realizar funciones del servicio pedido por la entidad(N+1). N-PCI (Informacin de control del protocolo) Informacin intercambiada entre entidades (N) utilizando una conexin (N1) para coordinar su operacin conjunta. N-IDU (Unidad de datos del interface) Es la informacin transferida entre dos niveles adyacentes,es decir, dos capas contiguas. Esta compuesta por: N-ICI (Informacin de control del interface) Informacin intercambiada entre una entidad (N+1) y una entidad (N) para coordinar su operacin conjunta. Datos de Interface-(N) Informacin transferida entre una entidad-(N+1) y una entidad-(N) y que normalmente coincide con la (N+1)-PDU.Transmisin de los datos

La capa de aplicacin recibe el mensaje del usuario y le aade una cabecera constituyendo as la PDU de la capa de aplicacin. La PDU se transfiere a la capa de aplicacin del nodo destino, este elimina la cabecera y entrega el mensaje al usuario. Para ello ha sido necesario todo este proceso: 1-Ahora hay que entregar la PDU a la capa de presentacin para ello hay que aadirla la correspondiente cabecera ICI y transformarla as en una IDU, la cual se transmite a dicha capa. 2-La capa de presentacin recibe la IDU, le quita la cabecera y extrae la informacin, es decir, la SDU, a esta le aade su propia cabecera (PCI) constituyendo as la PDU de la capa de presentacin. 3- Esta PDU es transferida a su vez a la capa de sesin mediante el mismo proceso, repitindose as para todas las capas. 4-Al llegar al nivel fsico se envan los datos que son recibidos por la capa fsica del receptor. 5-Cada capa del receptor se ocupa de extraer la cabecera, que anteriormente haba aadido su capa homloga, interpretarla y entregar la PDU a la capa superior. 6-Finalmente llegar a la capa de aplicacin la cual entregar el mensaje al usuario.

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Formato de los datos

Estos datos reciben una serie de nombres y formatos especficos en funcin de la capa en la que se encuentren, debido a como se describi anteriormente la adhesin de una serie de encabezados e informacin final. Los formatos de informacin son los que muestra el grfico:

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APDU: Unidad de datos en la capa de aplicacin. PPDU: Unidad de datos en la capa de presentacin. SPDU: Unidad de datos en la capa de sesin. TPDU:(segmento) Unidad de datos en la capa de transporte. Paquete: Unidad de datos en el nivel de red. Trama: Unidad de datos en la capa de enlace. Bits: Unidad de datos en la capa fsica.Operaciones sobre los datos

En determinadas situaciones es necesario realizar una serie de operaciones sobre las PDU para facilitar su transporte, bien debido a que son demasiado grandes o bien porque son demasiado pequeas y estaramos desaprovechando la capacidad del enlace.Segmentacin y reensamblaje [editar]

Hace corresponder a una (N)-SDU sobre varias (N)-PDU. El reensamblaje hace corresponder a varias (N)-PDUs en una (N)-SDU.Bloqueo y desbloqueo

El bloqueo hace corresponder varias (N)-SDUs en una (N)-PDU. El desbloqueo identifica varias (N)-SDUs que estn contenidas en una (N)-PDU.Concatenacin y separacin

La concatenacin es una funcin-(N) que realiza el nivel-(N) y que hace corresponder varias (N)-PDUs en una sola (N-1)-SDU. La separacin identifica varias (N)-PDUs que estn contenidas en una sola (N-1)-SDU. Vase tambin Familia de protocolos de Internet Enlaces externos Estndar ISO 7498-1:1994 (formato ZIP) Cybertelecom Layered Model of Regulation OSI Reference Model The ISO Model of Architecture for Open Systems Interconnection, Hubert Zimmermann, IEEE Transactions on Communications, vol. 28, no. 4, April 1980, pp. 425 - 432. Introduction to Data Communications Internetworking Basics MODELO DE REFERENCIA OSI - Interconexin de Sistemas Abiertos Ctedra Sistemas de Comunicaciones. Universidad Tecnolgica Nacional, Facultad Regional Mendoza, Argentina. 1.2 Su relacin con las redes industrialesING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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Red industrialDe Wikipedia, la enciclopedia libre Obtenido de "http://es.wikipedia.org/wiki/Red_industrial" INTRODUCCIN

Las redes de comunicaciones industriales deben su origen a la fundacin FieldBus (Redes de campo). La fundacin FieldBus, desarrollo un nuevo protocolo de comunicacin, para la medicin y control de procesos donde todos los instrumentos puedan comunicarse en una misma plataforma. Las comunicaciones entre los instrumentos de proceso y el sistema de control se basan principalmente en seales analgicas (neumticas de 3 a 15 psi en las vlvulas de control y electrnicas de 4 a 20 mA cc). Pero ya existen instrumentos digitales capaces de manejar gran cantidad de datos y guardarlos histricamente; su precisin es diez veces mayor que la de la seal tpica de 4-20 mA cc. En vez de transmitir cada variable por un par de hilos, transmiten secuencialmente las variables por medio de un cable de comunicaciones llamado bus. La tecnologa fieldbus (bus de campo) es un protocolo de comunicaciones digital de alta velocidad que esta creada para remplazar la clsica seal de 4-20 mA que an se utiliza en muchos de los sistemas DCS (Sistema de Control Distribuido) y PLC (Controladores Lgicos Programables), instrumentos de medida y transmisin y vlvulas de control. La arquitectura fieldbus conecta estos instrumentos con computadores que se usan en diferentes niveles de coordinacin y direccin de la planta. Muchos de los protocolos patentados para dichas aplicaciones tiene una limitante y es que el fabricante no permite al usuario final la interoperabilidad de instrumentos, es decir, no es posible intercambiar los instrumentos de un fabricante por otro similar. Es claro que estas tecnologas cerradas tienden a desaparecer ya que actualmente es necesaria la interoperabilidad de sistemas y aparatos y as tener la capacidad de manejar sistemas abiertos y estandarizados. Con el mejoramiento de los protocolos de comunicacin es ahora posible reducir el tiempo necesitado para la transferencia de datos, asegurando la misma, garantizando el tiempo de sincronizacin y el tiempo real de respuesta determinstica en algunas aplicaciones.LA TECNOLOGA DE BUSES DE CAMPO

Fsicamente podemos considerar a un bus como un conjunto de conductores conectando conjuntamente ms circuitos para permitir el intercambio de datos. Contrario a una conexin punto a punto donde solo dos dispositivos intercambian informacin, un bus consta normalmente de un nmero de usuarios superior, adems que generalmente un bus transmite datos en modo serial, a excepcin de algn protocolo de bus particular como SCSI, o IEEE-488 utilizado para interconexin de instrumentos de medicin, que no es el caso de los buses tratados como buses de campo. Para una transmisin serial es suficiente un nmero de cables muy limitado, generalmente son suficientes dos o tres conductores y la debida proteccin contra las perturbaciones externas para permitir su tendido en ambientes de ruido industrial.ING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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- El intercambio puede llevar a cabo por medio de un mecanismo estndar. Flexibilidad de extensin. - Conexin de mdulos diferentes en una misma lnea. Posibilidad de conexin de dispositivos de diferentes procedencias. - Distancias operativas superiores al cableado tradicional. - Reduccin masiva de cables y costo asociado. - Simplificacin de la puesta en servicio.Desventajas de un bus de campo

- Necesidad de conocimientos superiores. - Inversin de instrumentacin y accesorios de diagnstico. - Costos globales inicialmente superiores.Procesos de comunicacin por medio de bus

El modo ms sencillo de comunicacin con el bus es el sondeo cliente/servidor. Ms eficiente pero tambin ms costoso es el Token bus ( IEEE 802.4), desde el punto de vista fsico tenemos un bus lineal, desde el punto de vista lgico un token ring. El procedimiento token passing es una combinacin entre cliente/servidor y token bus. Todo servidor inteligente puede ser en algn momento servidor.ALGUNOS TIPOS DE BUS

La mayora de los buses trabajan en el nivel 1 con interfaz RS 485.ASI (Actuator Sensor Interface)

Es el bus ms inmediato en el nivel de campo y ms sencillo de controlar, consiste en un bus cliente/servidor con un mximo de 31 participantes, transmite por paquetes de solo 4 bits de dato. Es muy veloz, con un ciclo de 5 ms aproximadamente. Alcanza distancias de mximo 100 m.BITBUS

Es el ms difundido en todo el mundo, es cliente/servidor que admite como mximo 56 clientes, el paquete puede transmitir hasta 43 bytes de dato.PROFIBUS (PROcess FIeld BUS)

Es el estndar europeo en tecnologa de buses, se encuentra jerrquicamente por encima de ASI y BITBUS, trabaja segn procedimiento hbrido token passing, dispone de 31 participantes hasta un mximo de 127. Su paquete puede transmitir un mximo de 246 Bytes, y el ciclo para 31participantes es de aproximadamente 90 ms. Alcanza una distancia de hasta 22300 m.

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En la arquitectura OSI, fieldbus ocupa los niveles 1 (Fsico), 2 (Enlace de Datos) y 7 (Aplicacin); teniendo en cuenta que este ltimo no solo se encarga de la interfaz de usuario sino de aplicaciones especificas dependiendo de cada aplicacin.CLASIFICACION DE LAS REDES INDUSTRIALES.

Si se clasifican las redes industriales en diferentes categoras basndose en la funcionalidad, se har en:Buses Actuadores y Sensores

Inicialmente es usado un sensor y un bus actuador en conexin simple, dispositivos discretos con inteligencia limitada, como un foto sensor, un switch limitador o una vlvula solenoide, controladores y consolas terminales.Buses de Campo y Dispositivos

Estas redes se distinguen por la forma como manejan el tamao del mensaje y el tiempo de respuesta. En general estas redes conectan dispositivos inteligentes en una sola red distribuida.(Delta V de Emmerson) Estas redes ofrecen altos niveles de diagnstico y capacidad de configuracin, generalmente al nivel del poder de procesamiento de los dispositivos ms inteligentes. Son las redes ms sofisticadas que trabajan con control distribuido real entre dispositivos inteligentes, tal es el caso de FIELDBUS FOUNDATION.COMPONENTES DE LAS REDES INDUSTRIALES.

En grandes redes industriales un simple cable no es suficiente para conectar el conjunto de todos los nodos de la red. Deben definirse topologas y diseos de redes para proveer un aislamiento y conocer los requerimientos de funcionamiento.Bridge

Con un puente la conexin entre dos diferentes secciones de red, puede tener diferentes caractersticas elctricas y protocolos; adems puede enlazar dos redes diferentes.Repetidor

El repetidor o amplificador es un dispositivo que intensifica las seales elctricas para que puedan viajar grandes distancias entre nodos. Con este dispositivo se pueden conectar un gran nmero de nodos a la red; adems se pueden adaptar a diferentes medios fsicos como cable coaxial o fibra ptica.

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Un gateway es similar a un puente ya que suministra interoperabilidad entre buses y diferentes tipos de protocolos y adems las aplicaciones pueden comunicarse a travs de l.Enrutadores

Es un switch "Enrutador" de paquetes de comunicacin entre diferentes segmentos de red que definen la ruta.TOPOLOGIA DE REDES INDUSTRIALES

Los sistemas industriales usualmente consisten de dos o mas dispositivos, como un sistema industrial puede ser bastante grande debe considerarse la topologa de la red; las topologas ms comunes son: La Red Bus, Red Estrella y Red HbridaBENEFICIOS DE UNA RED INDUSTRIAL

- Reduccin de cableado (fsicamente) - Dispositivos inteligentes (funcionalidad y ejecucin) - Control distribuido (Flexibilidad) - Simplificacin de cableado de las nuevas instalaciones - Reduccin de costo en cableado y cajas de conexin Aplicable a todo tipo de sistema de manufactura - Incremento de la confiabilidad de los sistemas de produccin - Optimizacin de los procesos existentes.REDES INDUSTRIALES CON PLC

Muchos sistemas estn conformados por equipos de diferentes fabricantes y funcionan en diferentes niveles de automatizacin; adems, a menudo se encuentran distanciados entre s; pero sin embargo, se desea que trabajen en forma coordinada para un resultado satisfactorio del proceso. El objetivo principal es la comunicacin totalmente integrada en el sistema. Al usuario, esto le reporta la mxima flexibilidad ya que tambin puede integrar sin problemas productos de otros fabricantes a travs de las interfaces software estandarizadas. En los ltimos aos, las aplicaciones industriales basadas en comunicacin digital se han incrementado haciendo posible la conexin de sensores, actuadores y equipos de control en una planta de procesamiento. De esta manera, la comunicacin entre la sala de control y los instrumentos de campo se han convertido en realidad. La Comunicacin digital debe integrar la informacin provista por los elementos de campo en el sistema de control de procesos.SOLUCIONES CON ETHERNET

Aunque los buses de campo continuarn dominando las redes industriales, las soluciones basadas en Ethernet se estn utilizando cada vez ms en el sector de las tecnologas de automatizacin, donde las secuencias de procesos y produccin son controladas por un modelo cliente/servidor con controladores, PLC y sistemasING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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ERP (Planificacin de los recursos de la empresa), teniendo acceso a cada sensor que se conecta a la red. La implementacin de una red efectiva y segura tambin requiere el uso de conectores apropiados, disponibles en una amplia variedad y para soluciones muy flexibles. Los Gateway son dispositivos de capa de transporte; en donde la capa de aplicacin no necesariamente es software por lo general las aplicaciones son de audio (alarmas), vdeo (vigilancia), monitoreo y control (sensores), conversin anloga/digital y digital/analga. Para la programacin de gateway de alto nivel se utiliza el C++ y para la programacin menos avanzada se hace con hojas de clculo. Estos dispositivos pueden ser programados de tal forma que en caso de una emergencia o un simple cambio a otro proceso no se haga manualmente sino realmente automtico.CONCLUSION

Hoy en da las tecnologas que triunfan en el mercado son aquellas que ofrecen las mejores ventajas y seguridad a los clientes, cada vez se est acabando con tecnologas cerradas; que en un mundo en proceso de globalizacin, es imposible que sobrevivan. A nivel industrial se est dando un gran cambio, ya que no solo se pretende trabajar con la especificidad de la instrumentacin y el control automtico, sino que existe la necesidad de mantener histricamente informacin de todos los procesos, adems que esta informacin este tambin en tiempo real y que sirva para la toma de decisiones y se pueda as mejorar la calidad de los procesos. Las condiciones extremas a nivel industrial requieren de equipos capaces de soportar elevadas temperaturas, ruido excesivo, polvo, humedad y dems condiciones adversas; pero adems requiere de personal capaz de ver globalmente el sistema de control y automatizacin industrial junto con el sistema de red digital de datos. Enlaces externos redes de comunicacin industrial redes induatriales aplicaciones redes industruales con PLC

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UNIDAD 2 LAYERS FISICOS2.1 Los estandares RS232, IEEE-488 y RS485 RS-232From Wikipedia, the free encyclopedia Retrieved from "http://en.wikipedia.org/wiki/RS-232"

In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24.Scope of the standard

The Electronic Industries Alliance (EIA) standard RS-232-C[1] as of 1969 defines:

Electrical signal characteristics such as voltage levels, signaling rate, timing and slew-rate of signals, voltage withstand level, short-circuit behavior, maximum stray capacitance and cable length. Interface mechanical characteristics, pluggable connectors and pin identification. Functions of each circuit in the interface connector. Standard subsets of interface circuits for selected telecom applications.

The standard does not define such elements as

character encoding (for example, ASCII, Baudot or EBCDIC) the framing of characters in the data stream (bits per character, start/stop bits, parity) protocols for error detection or algorithms for data compression bit rates for transmission, although the standard says it is intended for bit rates lower than 20,000 bits per second. Many modern devices support speeds of 115,200 bps and above power supply to external devices.

Details of character format and transmission bit rate are controlled by the serial port hardware, often a single integrated circuit called a UART that converts data from parallel to serial form. A typical serial port includes specialized driver and receiver integrated circuits to convert between internal logic levels and RS-232 compatible signal levels.History

The original DTEs were electromechanical teletypewriters and the original DCEs were (usually) modems. When electronic terminals (smart and dumb) began to be used, they were often designed to be interchangeable with teletypes, and soING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices. Since application to devices such as computers, printers, test instruments, and so on were not considered by the standard, designers implementing an RS-232 compatible interface on their equipment often interpreted the requirements idiosyncratically. Common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes, patch boxes, test equipment, books, and other aids for the connection of disparate equipment. A common deviation from the standard was to drive the signals at a reduced voltage: the standard requires the transmitter to use +12V and -12V, but requires the receiver to distinguish voltages as low as +3V and -3V. Some manufacturers therefore built transmitters that supplied +5V and -5V and labeled them as "RS232 compatible." Later personal computers (and other devices) started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232compatible port was a standard feature for serial communications, such as modem connections, on many computers. It remained in widespread use into the late 1990s. While it has largely been supplanted by other interface standards in computer products, it is still used to connect older designs of peripherals, industrial equipment (such as based on PLCs), and console ports, and special purpose equipment such as a cash drawer for a cash register. The standard has been renamed several times during its history as the sponsoring organization changed its name, and has been variously known as EIA RS 232, EIA 232, and most recently as TIA 232. The standard continues to be revised and updated by the EIA and since 1988 the Telecommunications Industry Association (TIA)[2]. Revision C was issued in a document dated August 1969. Revision D was issued in 1986. The current revision is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. Changes since Revision C have been in timing and details intended to improve harmonization with the CCITT standard V.24, but equipment built to the current standard will interoperate with older versions.Limitations of the standard

Because the application of RS-232 has extended far beyond the original purpose of interconnecting a terminal with a modem, successor standards have been developed to address the limitations. Issues with the RS-232 standard include:

The large voltage swings and requirement for positive and negative supplies increases power consumption of the interface and complicates power supply design. The voltage swing requirement also limits the upper speed of a compatible interface. Single-ended signaling referred to a common signal ground limit the noise immunity and transmission distance. Multi-drop (meaning a connection between more than two devices) operation of an RS-232 compatible interface is not defined; while multi-drop

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"work-arounds" have been devised, they have limitations in speed and compatibility. Asymmetrical definitions of the two ends of the link make the assignment of the role of a newly developed device problematic; the designer must decide on either a DTE-like or DCE-like interface and which connector pin assignments to use. The handshaking and control lines of the interface are intended for the setup and takedown of a dial-up communication circuit; in particular, the use of handshake lines for flow control is not reliably implemented in many devices. No method for sending power to a device, while a small amount of current can be extracted from the DTR and RTS lines this can only be used for low power devices such as mice. While the standard recommends a connector and pinout, the connector is large by current standards.

Role in modern personal computers

PCI Express x1 card with one RS-232 port Main article: Serial port In the book PC 97 Hardware Design Guide[3], Microsoft deprecated support for the RS-232 compatible serial port of the original IBM PC design. Today, RS-232 is gradually being superseded in personal computers by USB for local communications. Compared with RS-232, USB is faster, has lower voltage levels, and has connectors that are simpler to connect and use. Both standards have software support in popular operating systems. USB is designed to make it easy for device drivers to communicate with hardware. However, there is no direct analog to the terminal programs used to let users communicate directly with serial ports. USB is more complex than the RS 232 standard because it includes a protocol for transferring data to devices. This requires more software to support the protocol used. RS 232 only standardizes the voltage of signals and the functions of the physical interface pins. Serial ports of personal computers are also often used to directly control various hardware devices, such as relays or lamps, since the control lines of the interface could be easily manipulated by software. This isn't feasible with USB which requires some form of receiver to decode the serial data. As an alternative, USB docking ports are available which can provide connectors for a keyboard, mouse, one or more serial ports, and one or more parallel ports. Corresponding device drivers are required for each USB-connected device to allow programs to access these USB-connected devices as if they were the original directly-connected peripherals. Devices that convert USB to RS 232 may not work with all software on all personal computers.Standard details ING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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In RS-232, data is sent as a time-series of bits. Both synchronous and asynchronous transmissions are supported by the standard. In addition to the data circuits, the standard defines a number of control circuits used to manage the connection between the DTE and DCE. Each data or control circuit only operates in one direction, that is, signaling from a DTE to the attached DCE or the reverse. Since transmit data and receive data are separate circuits, the interface can operate in a full duplex manner, supporting concurrent data flow in both directions. The standard does not define character framing within the data stream, or character encoding.

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Diagrammatic oscilloscope trace of voltage levels for ASCII "K" character (0x4b) with 1 start bit, 8 data bits, 1 stop bit Main article: Serial port The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels. Valid signals are plus or minus 3 to 15 volts. The range near zero volts is not a valid RS-232 level; logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance of OFF. Logic zero is positive, the signal condition is spacing, and has the function ON. The standard specifies a maximum open-circuit voltage of 25 volts; signal levels of 5 V,10 V,12 V, and 15 V are all commonly seen depending on the power supplies available within a device. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to +/-25 volts. The slew rate, or how fast the signal changes between levels, is also controlled. Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels. These also protect the device's internal circuitry from short circuits or transients that may appear on the RS-232 interface, and provide sufficent current to comply with the slew rate requirements for data transmission. Because both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero. This may also cause a hazardous ground loop.Connectors

RS-232 devices may be classified as Data Terminal Equipment (DTE) or Data Communications Equipment (DCE); this defines at each device which wires will be sending and receiving each signal. The standard recommended but did not make mandatory the D-subminiature 25 pin connector. In general, terminals have male connectors with DTE pin functions, and modems have female connectors with DCE pin functions. Other devices may have any combination of connector gender and pin definitions. Presence of a 25 pin D-sub connector does not necessarily indicate an RS-232C compliant interface. For example, on the original IBM PC, a male D-sub was an RS232C DTE port (with a non-standard current loop interface on reserved pins), but the female D-sub connector was used for a parallel Centronics printer port. Some personal computers put non-standard voltages or signals on their serial ports.

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Female 9 pin plug The standard specifies 20 different signal connections. Since most devices use only a few signals, smaller connectors can be used. For example, the 9 pin DE-9 connector was used by most IBM-compatible PCs since the IBM PC AT, and has been standardized as TIA-574. More recently, modular connectors have been used. Most common are 8 pin RJ45 connectors. Standard EIA/TIA 561 specifies a pin assignment, but the "Yost Serial Device Wiring Standard" invented by Dave Yost is common on Unix computers and newer devices from Cisco Systems. Many devices don't use either of these standards. 10 pin RJ-50 connectors can be found on some devices as well. Digital Equipment Corporation defined their own DECconnect connection system which was based on the Modified Modular Jack connector. This is a 6 pin modular jack where the key is offset from the center position. As with the Yost standard, DECconnect uses a symmetrical pin layout which enables the direct connection between two DTEs. Another common connector is the DH10 header connector common on motherboards and add-in cards which is usually converted via a cable to the more standard 9 pin DE-9 connector (and frequently mounted on a free slot plate or other part of the housing).

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The following table lists the commonly used RS-232 signals and common pin assignments DE-9 Cisc Signal Abbr DBEIA/TIA RJHirschman Alternate Dir. (TIAYost MMJ o RJType . 25 561 50 n RJ-45 s 574) 45 Common G Ground Transmitt TxD ed Data 7 5 3 2 4 6 5 3 1 8 4,5 6 3 6 2 7 1 8 9 7 5 4 3,4 2 5 1 6 4,5 3 6 2 7 4 3 5 -

Out 2 3

Received RxD In Data Data Terminal Ready

DTR Out 20 4 6 6 7

Data Set DSR In Ready Request To Send Clear Send Carrier Detect To RTS

Out 4

1 (Aux only) 8 (Aux only) -

CTS

In

5 8

8 1

7 2 1

8 7 -

3

-

DCD In In

10 2 -

Ring RI Indicator

22 9

The signals are labeled from the standpoint of the DTE device; TD, DTR, and RTS are generated by the DTE and RD, DSR, CTS, DCD, and RI are generated by the DCE. The ground signal is a common return for the other connections; it appears on two pins in the Yost standard but is the same signal. Connection of pin 1 (protective ground) and pin 7 (signal reference ground) is a common practice but not recommended. Use of a common ground is one weakness of RS-232. If the two pieces of equipment are far enough apart or on separate power systems, the ground will degrade between them and communications will fail; this is a difficult condition to trace. Note that EIA/TIA 561 combines DSR and RI, and the Yost standard combines DSR and DCD.

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Commonly-used signals are: Transmitted Data (TxD) Data sent from DTE to DCE. Received Data (RxD) Data sent from DCE to DTE. Request To Send (RTS) Asserted (set to 0) by DTE to prepare DCE to receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing the direction Clear To Send (CTS) Asserted by DCE to acknowledge RTS and allow DTE to transmit. Data Terminal Ready (DTR) Asserted by DTE to indicate that it is ready to be connected. If the DCE is a modem, this may "wake up" the modem, bringing it out of a power saving mode. This behaviour is seen quite often in modern PSTN and GSM modems. When this signal is de-asserted, the modem may return to its standby mode, immediately hanging up any calls in progress. Data Set Ready (DSR) Asserted by DCE to indicate an active connection. If DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be permanently asserted (set to 0), possibly by a jumper to another signal. Data Carrier Detect (DCD) Asserted by DCE when a connection has been established with remote equipment. Ring Indicator (RI) Asserted by DCE when it detects a ring signal from the telephone line. The standard defines RTS/CTS as the signaling protocol for flow control for data transmitted from DTE to DCE. The standard has no provision for flow control in the other direction. Various implementations of compatible ports may reassign other pins for flow control.Cables

Main article: Serial Cable Since the standard definitions are not always correctly applied, it is often necessary to consult documentation, test connections with a breakout box, or use trial and error to find a cable that works when interconnecting two devices. Connecting a fully-standard-compliant DCE device and DTE device would use a cable that connects identical pin numbers in each connector (a so-called "straight cable"). "Gender changers" are available to solve gender mismatches between cables and connectors. Connecting devices with different types of connectors requires a cable that connects the corresponding pins according to the table above. Cables with 9 pins on one end and 25 on the other are common. Manufacturers of equipment with RJ-45 connectors usually provide a cable with

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either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can work with multiple devices).

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For functional communication through a serial port interface, conventions of bit rate, character framing, communications protocol, character encoding, data compression, and error detection, not defined in RS 232, must be agreed to by both sending and receiving equipment. For example, consider the serial ports of the original IBM PC. This implementation has an integrated circuit UART, often 16550 UART, using asynchronous start-stop character formatting with 7 or 8 data bits per frame, usually ASCII character coding, and data rates programmable between 75 bits per second and 115,000 bits per second. Data rates above 20,000 bits per second are out of the scope of the standard, although higher data rates are sometimes used by commercially manufactured equipment. In the particular case of the IBM PC, baud rates were programmable with arbitrary values, so that a PC could be connected to, for example, MIDI music controllers (31,250 bits per second) or other devices not using the rates typically used with modems. Since most devices do not have automatic baud rate detection, users must manually set the baud rate (and all other parameters) at both ends of the RS-232 connection.RTS/CTS handshaking

The standard RS-232 use of the RTS and CTS lines is asymmetrical. The DTE asserts RTS to indicate a desire to transmit to the DCE. The DCE asserts CTS in response to grant permission. This allows for half-duplex modems that disable their transmitters when not required, and must transmit a synchronization preamble to the receiver when they are re-enabled. There is no way for the DTE to indicate that it is unable to accept data from the DCE. A non-standard symmetrical alternative is widely used: CTS indicates permission from the DCE for the DTE to transmit, and RTS indicates permission from the DTE for the DCE to transmit. The "request to transmit" is implicit and continuous. Thus, with this alternative usage, one can think of RTS asserted (logic 0) meaning "ready to receive characters" from the DTE, rather than a "request to transmit" to the DCE.3-wire and 5-wire RS-232

A minimal "3-wire" RS-232 connection consisting only of transmit data, receive data, and ground, is commonly used when the full facilities of RS-232 are not required. When only flow control is required, the RTS and CTS lines are added in a 5-wire version.Seldom used features

The EIA-232 standard specifies connections for several features that are not used in most implementations. Their use requires the 25-pin connectors and cables, and of course both the DTE and DCE must support them.

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The DTE or DCE can specify use of a "high" or "low" signaling rate. The rates as well as which device will select the rate must be configured in both the DTE and DCE. The prearranged device selects the high rate by setting pin 23 to ON.Loopback testing

Many DCE devices have a loopback capability used for testing. When enabled, signals are echoed back to the sender rather than being sent on to the receiver. If supported, the DTE can signal the local DCE (the one it is connected to) to enter loopback mode by setting pin 18 to ON, or the remote DCE (the one the local DCE is connected to) to enter loopback mode by setting pin 21 to ON. The latter tests the communications link as well as both DCE's. When the DCE is in test mode it signals the DTE by setting pin 25 to ON. A commonly used version of loopback testing doesn't involve any special capability of either end. A hardware loopback is simply a wire connecting complementary pins together in the same connector. See loopback. Loopback testing is often performed with a specialized DTE called a Bit Error Rate Tester (BERT).Timing signals

Some synchronous devices provide a clock signal to synchronize data transmission, especially at higher data rates. Two timing signals are provided by the DCE on pins 15 and 17. Pin 15 is the transmitter clock, or send timing (ST); the DTE puts the next bit on the data line (pin 2) when this clock transitions from OFF to ON (so it is stable during the ON to OFF transition when the DCE registers the bit). Pin 17 is the receiver clock, or receive timing (RT); the DTE reads the next bit from the data line (pin 3) when this clock transitions from ON to OFF. Alternatively, the DTE can provide a clock signal, called transmitter timing (TT), on pin 24 for transmitted data. Again, data is changed when the clock transitions from OFF to ON and read during the ON to OFF transition. TT can be used to overcome the issue where ST must traverse a cable of unknown length and delay, clock a bit out of the DTE after another unknown delay, and return it to the DCE over the same unknown cable delay. Since the relation between the transmitted bit and TT can be fixed in the DTE design, and since both signals traverse the same cable length, using TT eliminates the issue. TT may be generated by looping ST back with an appropriate phase change to align it with the transmitted data. ST loop back to TT lets the DTE use the DCE as the frequency reference, and correct the clock to data timing.Secondary channel

Data can be sent over a secondary channel (when implemented by the DTE and DCE devices), which is equivalent to the primary channel. Pin assignments are described in following table:ING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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Signal Common Ground Secondary (STD) Secondary (SRD) Transmitted Received Data Data

Pin 7 (same primary) 14 16 as

Secondary Request To Send 19 (SRTS) Secondary (SCTS) Secondary (SDCD)Related standards

Clear Carrier

To

Send Detect

13 12

Other serial signaling standards may not interoperate with standard-compliant RS232 ports. For example, using the TTL levels of near +5 and 0 V puts the mark level in the undefined area of the standard. Such levels are sometimes used with NMEA 0183-compliant GPS receivers and depth finders. 20 mA current loop uses the absence of 20 mA current for high, and the presence of current in the loop for low; this signaling method is often used for long-distance and optically isolated links. Connection of a current-loop device to a compliant RS232 port requires a level translator; current-loop devices are capable of supplying voltages in excess of the withstand voltage limits of a compliant device. The original IBM PC serial port card implemented a 20 mA current-loop interface, which was never emulated by other suppliers of plug-compatible equipment. Other serial interfaces similar to RS-232:

RS-422 (a high-speed system similar to RS-232 but with differential signaling) RS-423 (a high-speed system similar to RS-422 but with unbalanced signaling) RS-449 (a functional and mechanical interface that used RS-422 and RS-423 signals - it never caught on like RS-232 and was withdrawn by the EIA) RS-485 (a descendant of RS-422 that can be used as a bus in multidrop configurations) MIL-STD-188 (a system like RS-232 but with better impedance and rise time control) EIA-530 (a high-speed system using RS-422 or RS-423 electrical properties in an EIA-232 pinout configuration, thus combining the best of both; supersedes RS-449) TIA-574 (standardizes the 9-pin D-subminiature connector pinout for use with EIA-232 electrical signalling, as originated on the IBM PC/AT)INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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See also

Asynchronous start-stop List of device bandwidths

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References 1. ^ Electronics Industries Association, "EIA Standard RS-232-C Interface BetweenData Terminal Equipment and Data Communication Equipment Employing Serial Data Interchange", August 1969, reprinted in Telebyte Technology Data Communication Library, Greenlawn NY, 1985, no ISBN 2. ^ TIA Web site 3. ^ (1997) PC 97 Hardware Design Guide. Redmond,Washington, USA: Microsoft Press. ISBN 1-57231-381-1.

External links

Wikibooks' Serial Programming has more about this subject: Serial Programming:RS-232 Connections

RS-232 tutorial Yost Serial Device Wiring Standard Serial Port Basics RS232 serial port info

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EIA-485 (formerly RS-485 or RS485) is an OSI model physical layer electrical specification of a two-wire,[1] half-duplex, multipoint serial connection. The standard specifies a differential form of signalling. The difference between the wires voltages is what conveys the data. One polarity of voltage indicates a logic 1 level, the reverse polarity indicates logic 0. The difference of potential must be at least 0.2 volts for valid operation, but any applied voltages between +12 V and -7 volts will allow correct operation of the receiver. EIA-485 only specifies electrical characteristics of the driver and the receiver. It does not specify or recommend any data protocol. EIA-485 enables the configuration of inexpensive local networks and multidrop communications links. It offers high data transmission speeds (35 Mbit/s up to 10 m and 100 kbit/s at 1200 m). Since it uses a differential balanced line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres). In contrast to EIA-422, which has a single driver circuit which cannot be switched off, EIA-485 drivers need to be put in transmit mode explicitly by asserting a signal to the driver. This allows EIA-485 to implement linear topologies using only two wires. The equipment located along a set of EIA-485 wires are interchangeably called nodes, stations and devices. The recommended arrangement of the wires is as a connected series of point-topoint (multidropped) nodes, a line or bus, not a star, ring, or multiply-connected network. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. Without termination resistors, reflections of fast driver edges can cause multiple data edges that can cause data corruption. Termination resistors also reduce electrical noise sensitivity due to the lower impedance, and bias resistors (see below) are required. The value of each termination resistor should be equal to the cable impedance (typically, 120 ohms for twisted pairs). Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. Somewhere along the set of wires, powered resistors are established to bias each data line/wire when the lines are not being driven by any device. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. Often in a master-slave arrangement when one device dubbed "the master" initiates all communication activity, the master device itself provides the bias and not the slave devices. In this configuration, the master device is typically centrally located along the set of EIA-485 wires, so it would be two slave devices located atING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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the physical end of the wires that would provide the termination. The master device would provide termination if it itself was located at a physical end of the wires, but that is often a bad design as the master would be better located at a halfway point between the slave devices. Note that it is not a good idea to apply the bias at multiple node locations, because, by doing so, the effective bias resistance is lowered, which could possibly cause a violation of the EIA-485 specification and cause communications to malfunction. By keeping the biasing with the master, slave device design is simplified and this situation is avoided. EIA-485, like EIA-422 can be made full-duplex by using four wires, however, since EIA-485 is a multi-point specification, this is not necessary in many cases. EIA-485 and EIA-422 can interoperate with certain restrictions. RS-485 can be used to communicate with remote devices at distances up to 4000 ft (1200 m) at speeds of up to 100 kbit/s at this distance. Converters between RS232 and RS485, USB and RS485, Ethernet and RS485 are available to allow your PC to communicate with remote devices. By using "Repeaters" and "MultiRepeaters" very large RS485 networks can be formed. The Application Guidelines for TIA/EIA-485-A has one diagram called "Star Configuration. Not recommended." Using an RS485 "Multi-Repeater" can allow for "Star Configurations" with "Home Runs" (or multi-drop) connections similar to Ethernet Hub/Star implementations (with greater distances). Hub/Star systems (with "Multi-Repeaters") allow for very maintainable systems, without violating any of the RS485 specifications. Repeaters can also be used to extend the distance and/or number of nodes on a network.Uses of EIA-485

SCSI-2 and SCSI-3 (for instance) use this specification to implement the physical layer. EIA-485 is often used with common UARTs to implement low-speed data communications in commercial aircraft cabins. For example, some passenger control units use it. It requires minimal wiring, and can share the wiring among several seats. It therefore reduces the system weight. EIA-485 also sees some use in programmable logic controllers and on factory floors in order to implement proprietary data communications. Since it is differential, it resists electromagnetic interference from motors and welding equipment. EIA-485 is used in large sound systems, as found at music events and theatre productions, for remotely controlling high-end sound-processing equipment from a standard computer running special software. The EIA-485 link is typically implemented over standard XLR cables more usually used for microphones, and so can be run between stage and control desk without laying special cables. EIA-485 also is used in Building automation as the simple bus wiring and long cable length is ideal for joining remote devices. EIA-485 also is used to control theatrical and disco lighting where it is used as the communications protocol for DMX signals.

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EIA-485 is used to control video surveillance cameras. Typically wiring runs from a central controller to a number of cameras which have stepper motors for pan, tilt and zoom. One or more joysticks are connected to the controller and each camera is assigned an address. There appear to be a number of vendor defined protocols for communication of the actual movement requests. This standard is now administered by the TIA and is titled TIA-485-A, Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems (ANSI/TIA/EIA-485-A-98) (R2003), indicating that the standard was reaffirmed without technical changes in 2003.Connectors

EIA-485 does not specify any connector. Pin labelling The RS485 differential line consists of two pins: A aka '' aka TxD-/RxD- aka inverting pin which is negative (compared to B) when the line is idle (ie data is 1). B aka '+' aka TxD+/RxD+ aka non-inverting pin which is positive (compared to A) when the line is idle (ie data is 1). These names are all in use on various equipment, but the actual standard released by EIA only uses the names A and B. However, despite the unambiguous standard there is much confusion about which is which: The RS485 signalling specification states that signal A is the inverting or '-' pin and signal B is the non-inverting or '+' pin. [1] The same naming is specified in the NMEA standards. This is in conflict with the A/B naming used by a number of differential transceivers manufacturers, including the Texas Instruments application handbook on RS422/485 communications (A=non-inverting, B=inverting). These manufacturers are incorrect, but their practice is in a widespread use. Therefore, care must be taken when using A/B naming. In addition to the A and B connections, the EIA standard also specifies a third interconnection point called C, which is the common ground.Waveform example

The graph below shows potentials of the '+' and '' pins of an RS-485 line during transmission of an RS-485 byte:

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^ Why you need 3 wires for 2 (two) wire RS485See also

Wikibooks has a Programming:RS-485 Technical Manual RS-232 RS-422 RS-423 Modbus Profibus FieldbusExternal links

book

on

the

topic

of

Serial

Guidelines for Proper Wiring of an RS-485 (TIA/EIA-485-A) Network Technical library of RS-485 articles and application notes RS232 to RS485 cable scheme RS422 and RS485 Standards Overview Practical information about implementing RS485

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Interface Converter RS232 to RS485 cable pinoutElectrically isolated RS485 communication interface to the PC serial port

EIA-485 cable usually made with twisted pair (like EIA-422) and may span up to 1200 metres. The recommended arrangement of the wires is as a connected series of point-to-point nodes, a line or bus. Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. The value of each termination resistor should be equal to the cable impedance (typically, 120 ohms for twisted pairs). ING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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PC RS485 InterfaceThis interface circuit provides electrically isolated RS485 communication inteface to the PC serial port the isolation circuit protect the PC from direct connection to hazardous voltages.

M Asim Khan, [email protected]

Figure 1: Circuit Diagram of Isolated RS485 Interface

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Figure 1 shows the circuit diagram of RS485 interface. Connector K1 is linked to the serial port of the PC, power to the PC side of the circuit is derived from the signal lines DTR and RTS. Positive supply is derived from RTS and negative supply from the DTR line. The RTS line is also used to control the data direction of RS485 driver IC U4. Optical isolation is achieved by optocouplers U1, U2 and U3. Opto U1 is used to control the data direction of U4 opto U2 provide RXD line isolation while opto U3 provide TXD line isolation. The other side of the isolator carries TTL levels. This side is powered by an unregulated dc supply between 9V and 18V dc. IC U5 provide 5V regulated output and IC U4 provide the RS485 bus interface. The TXD and RXD lines status are provided by data indicating LEDs. The interface has been tested at the baud rate of 19.2k baud. For Data Reception RTS = 1 (at +ve level) For Data Transmition RTS = 0 (at -ve level) DTR line is always set to 0 (at -ve level) Figure 2 & 3 shows the component layout of the isolator pcb and the track patterns respectively.

Figure 2: Component layout of the Isolator PCBING. ALFONSO PEREZ GARCIA INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

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Figure 3: Track patterns of the Isolator PCB

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Component details of the project.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 QUANTIT Y 4 1 1 3 2 2 1 1 1 3 2 2 3 1 2 1 2 1 1 1 DESIGNATOR C1,C2,C3,C6 C4 C5 D1,D2,D3 D4,D5 D7,D6 D8 K1 K2 R1,R2,R3 R7,R4 R5,R8 R9,R12 R6 R11,R10 R13 U3,U1 U2 U4 U5 DESCRIPTION 100nF 10uF 16V 470uF 25V 1N4148 LED RED 3mm TRANSIL 6.8V 1N4003 DB9 R/A PCB PLUG PCB TERMINAL BLOCK 4 WAY 1K8 4K7 1K 150R 680R 10R 120R H11L1 OPTO-ISOLATOR CNY17-3 OPTO-ISOLATOR MAX487, SN75176B LM7805

2 July 2001

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IEEE-488From Wikipedia, the free encyclopedia Retrieved from "http://en.wikipedia.org/wiki/IEEE-488"

IEEE-488 is a short-range, digital communications bus specification that has been in use for over 30 years. Originally created for use with automated test equipment, the standard is still in wide use for that purpose. IEEE-488 is also commonly known as HP-IB (Hewlett-Packard Instrument Bus) and GPIB (General Purpose Interface Bus). IEEE-488 allows up to 15 devices to share a single 8-bit parallel electrical bus by daisy chaining connections. The slowest device participates in control and data transfer handshakes to determine the speed of the transaction. The maximum data rate is about one Mbyte/s in the original standard, and about 8 Mbyte/s with later extensions. The IEEE-488 bus employs 16 signal lines eight bi-directional used for data transfer, three for handshake, and five for bus management plus eight ground return lines.IEEE-488 / HP-IB / GPIB Type Designer Designed Manufactur er Produced External Data signal General purpose data bus Production history Hewlett-Packard late 1960s standardized in 1975 Hewlett-Packard 1960s to present Specifications yes Parallel data bus with handshaking Width Bandwidth 8 bits 1 Mbyte/s (later extended to 8 Mbyte/s) 15 Parallel IEEE-488 stacking connectors

Max devices Protocol Cable Pins Connector 20 meters max

24 (8 data, 5 bus management, 3 handshake, 8 ground) 24-pin Amphenol-designed micro ribbon

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Pin out

A female IEEE-488 connector Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8 Pin 9 Pin 10 Pin 11 Pin 12 Pin 13 Pin 14 Pin 15 Pin 16 Pin 17 Pin 18 Pin 19 Pin 20 Pin 21 Pin 22 Pin 23 Pin 24 DIO1 DIO2 DIO3 DIO4 EOI DAV NRFD NDAC IFC SRQ ATN SHIELD DIO5 DIO6 DIO7 DIO8 REN GND GND GND GND GND GND Logic ground Data input/output bit. Data input/output bit. Data input/output bit. Data input/output bit. Remote enable. (wire twisted with DAV) (wire twisted with NRFD) (wire twisted with NDAC) (wire twisted with IFC) (wire twisted with SRQ) (wire twisted with ATN) Data input/output bit. Data input/output bit. Data input/output bit. Data input/output bit. End-or-identify. Data valid. Not ready for data. Not data accepted. Interface clear. Service request. Attention.

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In the late 1960s, Hewlett-Packard (HP), a manufacturer of test and measurement instruments[1], such as digital multimeters and logic analyzers, developed the HP Interface Bus (HP-IB) to enable easier interconnection between instruments and controllers such as computers. Early HP 9800 series[2] desktop computers used HP-IB to connect peripherals (printers, plotters, disk drives etc.). The bus was relatively easy to implement using the technology at the time, using a simple parallel electrical bus and several individual control lines; the interface functions could be implemented in simple TTL logic[3] Other manufacturers copied HP-IB, calling their implementation the General Purpose Interface Bus (GPIB). In 1975 the bus was standardized by the Institute of Electrical and Electronics Engineers as the IEEE Standard Digital Interface for Programmable Instrumentation, IEEE-488-1975 (now 488.1). IEEE-488.1 formalized the mechanical, electrical, and basic protocol parameters of GPIB, but said nothing about the format of commands or data. The IEEE-488.2 standard, Codes, Formats, Protocols, and Common Commands for IEEE-488.1 (June 1987), provided for basic syntax and format conventions, as well as device-independent commands, data structures, error protocols, and the like. IEEE-488.2 built on -488.1 without superseding it; equipment can conform to -488.1 without following -488.2. While IEEE-488.1 defined the hardware, and IEEE-488.2 defined the syntax, there was still no standard for instrument-specific commands. Commands to control the same class of instrument (e.g., multimeters) would vary between manufacturers and even models. A standard for device commands, SCPI, was introduced in the 1990s. Due to the late introduction, it has not been universally implemented. National Instruments introduced a backwards-compatible extension to IEEE-488.1, originally known as HS-488. It increased the maximum data rate to 8 Mbyte/s, although the rate decreases as more devices are connected to the bus. This was incorporated into the standard in 2003, as IEEE-488.1-2003. In addition to the IEEE, several other standards committees have adopted HP-IB. The American National Standards Institute's corresponding standard is known as ANSI Standard MC 1.1, and the International Electrotechnical Commission has its IEC Publication 625-1.Applications

At the outset, HP-IB's designers did not specifically plan for IEEE-488 to be a standard peripheral interface for general-purpose computers. By 1977 the Commodore PET/CBM range of educational/home/personal computers connected their disk drives, printers, modems, etc, by IEEE-488 bus. All of Commodore's post-PET/CBM 8-bit machines, from the VIC-20 to the C128, utilized a proprietary 'serial IEEE-488' for peripherals, with round DIN connectors instead of the heavy-

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duty HP-IB plugs or a card-edge connector plugging into the motherboard (for PET computers). Hewlett-Packard and Tektronix also used IEEE-488 as a peripheral interface to connect disk drives, tape drives, printers, plotters etc. to their workstation products and HP's HP 2100[4] and HP 3000[5] minicomputers. While the bus speed was increased to 10 MB/s for such applications, the lack of command protocol standards limited third-party offerings and interoperability, and later, faster, open standards such as SCSI eventually superseded IEEE-488 for peripheral access. Additionally, some of HP's advanced pocket calculators/computers of the 1980s, such as the HP-41 and HP-71B series, could work with various instrumentation via an optional HP-IB interface. The interface would connect to the calculator via an optional HP-IL module.Signals bus line DIO1DIO8 description Data input/output bits. These 8 lines are used to read and write the 8 bits of a data or command byte that is being sent over the bus. Not ready for data. NRFD is a handshaking line asserted by listeners to indicate they are not ready to receive a new data byte. Data valid. This is a handshaking line, used to signal that the value being sent with DIO1-DIO8 is valid. During transfers the DIO1-DIO8 lines are set, then the DAV line is asserted after a delay called the 'T1 delay'. The T1 delay lets the data lines settle to stable values before they are read. Not data accepted. NDAC is a handshaking line asserted by listeners to indicate they have not yet read the byte contained on the DIO lines. Attention. ATN is asserted to indicate that the DIO lines contain a command byte (as opposed to a data byte). Also, it is asserted with EOI when conducting parallel polls. End-or-identify. This line is asserted with the last byte of data during a write, to indicate the end of the message. It can also be asserted along with the ATN line to conduct a parallel poll. Interface clear. The system controller can assert this line (it should be asserted for at least 100 microseconds) to reset the bus and make itself controller-in-charge. Remote enable. Asserted by the system controller, it enables devices to enter remote mode. When REN is asserted (low), a device will enter remote mode when it is addressed by the controller. When REN is false (high), all devices will immediately return to local mode.

NRFD

DAV

NDAC

ATN

EOI

IFC

REN

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Service request. Devices on the bus can assert this line to request service from the controller-in-charge. The controller can then poll the devices until it finds the device requesting service, and perform whatever action is necessary.

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IEEE-488 uses 24-pin Amphenol-designed micro ribbon connectors (often incorrectly termed Centronics-type), most commonly in a stackable male/female combination that allows for easy daisy-chaining by stacking cables. Mechanical considerations limit the number of stacked connectors to four or less. They are held in place by screws, which come in UTS (now largely obsolete) or metric (M3.50.6) threads. By convention, metric screws are colored black, as the two threads do not mate. Total cable length is limited to 20 metres, although nonstandard "bus extender" devices are available.IEC-625

The IEC-625 standard prescribes the use of 25-pin D-subminiature connectors (the same are used for parallel ports on PCs). This standard did not gain significant market acceptance against the established 24-pin connector. See also HP series 80 Rocky Mountain BASIC References ^ This portion of the company was later spun-off as Agilent Technologies ^ HP 9815 98135A HP-IB Interface ^ Examples: HP 59501 Power Supply Programmer, HP 59306A Relay Actuator ^ HP 2100 59310A HP-IB Interface ^ HP 3000 27113A CIO HP-IB Interface IEEE Standards IEEE-488.1: Standard Digital Interface for Programmable Instrumentation IEEE-488.2: Standard Codes, Formats, Protocols, and Common Commands for Use With IEEE-488.1 Press release on IEEE 488.1-2003, which allows for higher speeds External links A GPIB tutorial (mirror) from TransEra Corporation Explanation of connector stacking GPIB (2 BitsING. ALFONSO PEREZ GARCIA

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>Frame Format Start of Frame Identifier RTR Bit Control Field Data Field CRC Sequence CRC Delimiter Acknowledge Ack Delimiter End of Frame Interframe Space

INSTITUTO TECNOLOGICO DE SAN LUIS POTOSI

UNIDAD 7 DEVICENET Reference[10]

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Upon transmitting the first packet of data, the "Start of Frame" bit is sent to synchronize all receivers on the network. The CAN identifier (denoted from 0-63) and RTR bit combine to set priority at which the data can be accessed or changed. Lower identifiers have priority over higher identifiers. In addition to transmitting this data to other devices, the device also monitors the data sent. This redundancy validates the data transmitted and eliminates simultaneous transmissions. If a node is transmitting at the same time as another node, the node with the lower 11 bit identifier will continue to transmit while the device with the higher