Comunicación Serie Normas y Protocolos

TIA/EIA-232-F ITU.V28

TIA/EIA-232-F ITU.V28

TIA/EIA-232-F ITU.V28 Max Voltaje ±25V Longitud del Cable 15 a 20 m Max Slew Rate 30 v/μs Capacidad Maxima: 2500 pF

Conversores TTL / 232

Conversores TTL / 232

TIA/EIA-232-F ITU.V28

TIA/EIA-232-F ITU.V28

TIA/EIA-232-F ITU.V28

Hardware Flow Control

Hardware Flow Control

Hardware Flow Control

Hardware Flow Control 1The computer sets DTR to indicate that it wants to make use of the modem. 2The modem signals that it is ready and that a connection has been established. 3The computer requests permission to send. 4The modem informs the computer that it is now ready to receive data from the computer and send it through the phone wires. 5The modem drops CTS to signal to the computer that its internal buffers are full; the computer stops sending characters to the modem. 6The buffers of the modem have been purged, so the computer may continue to send data. 7This situation is not clear; either the computer's buffers are full and it wants to inform the modem of this, or it doesn't have any more data to be send to the modem. Normally, modems are configured to stop any transmission between the computer and the modem when RTS is dropped. 8The modem acknowledges RTS by dropping CTS. 9RTS is again raised by the computer to re-establish data transmission. 10The modem shows that it is ready to do its job. 11No more data is to be sent. 12The modem acknowledges this. 13DTR is dropped by the computer; this causes most modems to hang up. After hang-up, the modem acknowledges with DSR low. If the connection breaks, the modem also drops DSR to inform the computer about it.

Differential Signaling

Differential Signaling

Differential Signaling Single Ended High State= Vs Low State=0 High-Low=Vs-0=Vs Differential High State V+= Vs V-=0 ∆high= V+ - V- = Vs Low State V+= 0 V-=Vs ∆Low= V+ - V- = -Vs High State - Low State = Vs – ( - Vs )=2Vs

Differential Signaling Diferencial requiere solo la mitad de la variación de tensión que en el caso de la transmisión single ended. Por lo tanto se requiere una menor corriente de carga de las capacidades parasitas (dv/dt) Como consecuencia es mas rápido

RS-422 Norma EIA/TIA-422 Diferencial hasta 10Mb/s y 1500 m. Topología de Red: Punto a punto Multipunto

RS-422

RS-485

Protocolos de enlace de datos XON/XOFF

Protocolos de enlace de datos Topología de redes Point to Point

Protocolos de enlace de datos Topología de redes Multidrop

Protocolos de enlace de datos HDLC (High Level Data Link Control) Topología de redes Multipoint (RS-485)

Protocolos de enlace de datos HDLC (High Level Data Link Control) Topología de redes Multipoint(RS-422)

Protocolos de enlace de datos

Protocolos de enlace de datos

Protocolos de enlace de datos HDLC Frame Format Flag: Fija los limites de la trama (Start / End ) Address: Identifica los nodos remotos Control: Propósito de la trama Information: Datos del usuario FCS: Frame check Secuence CRC o LRC (8,16 o 32 bits)

Protocolos de enlace de datos HDLC Framing Caracteres de control: STX (Start of Text) 0x02 , ETX 0x03 (End of Text) Octetos con valor < 0x20 son no imprimibles Carácter Especial para transmitir caracteres no imprimibles de control DLE : Data Link Escape : 0x10 Inicio de trama: DLE STX Fin de trama: DLE ETX Todos los DLE ocurren de a pares salvo en el principio y final de trama

Protocolos de enlace de datos Byte Stuffing in PPP Flag es: 0x7E Carácter de escape :0x7D Toda ocurrencia dentro de la trama del Flag o el carácter de escape es reemplazado por 0x7D + el carácter original XOR 0x20. Ej: 0x7D -> 0x7D + ( 0x7D xor 0x20 ) = 0x7D + 0x5D

Protocolos de enlace de datos OSI Model

Protocolos de enlace de datos HDLC (Custom) SOM DATA LRC EOM SYNC ADDRESS SOM : Start of Message = 111A4A3A2A1A0 = SYNC | Address EOM : End Of Message = 0xF8 SYNC: Frame Sync= 11100000b=0xE0 LRC : Longitudinal Redundancy Check: SOM xor DATA xor EOM

Protocolos de enlace de datos HDLC (High Level Data Link Control) Start of Message = 111A4A3A2A1A0 Ejemplo: 0xE0  SOM for Address 0 0xE1  SOM for Address 1 ------------------------------------ 0xF7  SOM for Address 23 0xF8  EOM 0xF9 TCH If DATA ≥ 0xE0 Then Send: TCH + DATA xor TCH LRC= SOM xor DATA xor EOM

Protocolos de enlace de datos HDLC (FSM Recepcion) ILDE SOM SOM S1 Any,Save TCH, XOR and Save EOM, Eval LRC S2 LRC FAILED Messaje OK LRC OK

Protocolos de enlace de datos HDLC (High Level Data Link Control) “Fast Poll” MASTER SLAVE Caso A SOM + SOM SOM (No New Data) Caso B SOM + SOM SOM+DATA+LRC+EOM (Slave has Data) Caso C SOM+DATA+LRC+EOM SOM+DATA+LRC+EOM (Normal Transfer)