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EET 450 - Advanced Digital. Chapter 21 Serial Ports. Serial Communications. Contrasting with parallel communications - the individual bits are transmitted one at a time. Uses time division multiplexing versus space division multiplexing. Modern Serial. Options classic - RS 232

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Eet 450 advanced digital

EET 450 - Advanced Digital

Chapter 21

Serial Ports


Serial communications
Serial Communications

  • Contrasting with parallel communications - the individual bits are transmitted one at a time.

    • Uses time division multiplexing versus space division multiplexing


Modern serial
Modern Serial

  • Options

    • classic - RS 232

    • ACCESS.bus

    • IrDA optical

    • Universal Serial bus

    • P1394


Transfer rate characteristics
Transfer rate/characteristics

  • RS232 - standard for years

    • max rate 115,200 bps

    • uses twisted pair

    • 1 device per port

  • ACCESS.bus - inexpensive option

    • max rate 100 Kbps

    • 4-wire shielded cable

    • 125 devices per port




Basic serial communications
Basic Serial Communications

  • Clocking

    • Synchronous communications

      • bits are synchronized to a separate clock signal

    • Asynchronous

      • Bits are time from the start of a period - no universal clock

    • Isosynchronous communications

      • time critical data


Serial communications1
Serial Communications

  • Frames

    • bits are collected into frames of data

    • frame is delineated with stop/start bits

    • Within the frame is data and error correction information.


Serial communications2
Serial Communications

  • Each byte of data is encapsulated in a frame.

    • Provides timing & error checking

  • Packets - blocks of bytes can be compiled into a packet of data. For example

Address

Description

Data

Error Chk


Packets
Packets

  • Packets range in size from a few bytes to a few kbytes. (256-2048 per text)

  • May include routing information, commands, and error checking (CRC)

    • This is overhead that decreases overall throughput


Rs 232c
RS-232C

  • The traditional COM port

  • Port speeds are restricted by internal clock of PC 150:300:600:1200:2400:4800:9600

    19200:38400:57600:115200

  • physical connection

    • Standard connectors

      • DB25

      • DB9


Rs 232c1
RS-232C

  • Signals include

    • Transmit Data

      • from the Data Terminal Equipment

    • Receive Data

      • to the DTE (from DCE)

    • Data Terminal Ready

      • From DTE to DCE - ready to receive


Rs 232c2
RS-232C

  • Data Set Ready

    • DSR - to DTE from DCE - ready

  • Request to send

    • RTS - opposite of DSR

  • Clear to send

    • CTS to DTE opposite of DTR


  • Rs 232c3
    RS-232C

    • Carrier Detect

      • For modem signaling - the modem carrier signal is detected

    • Ring Indicator

      • Again for modems - indicates a ring signal on incoming line


    Flow control
    Flow Control

    • Two methods of controlling the sending/receiving of data on a serial connection.

    • Hardware -

      • uses signal wires from physical layer above

    • Software -

      • uses control signals - either XON/XOFF or ETX/ACK


    Cables
    Cables

    • designed to run on unshielded twisted pair (UTP)

    • Shielded cable can extend effective range

    • Wiring depends on flow control

      • Software - 3 wires needed (XMIT/RCV/Ground)

      • Hardware - all wires as above

    • Connectors - DB25 or DB9 (m/f)


    Cables1
    Cables

    • Crossover cable

      • uses available signals to lie to the ports - allows for software control only.

    • Null Modem is the common name, though this is more properly a test plug.


    Chips
    Chips

    • UART - Universal Asynchronous Receive r/Transmitter

    • 8250

    • 16450

    • 16550


    Access bus
    Access.bus

    • Allows 125 devices to a single port

    • Simple - Slow

    • Software flow control

    • Three layers

      • Physical

      • Base

      • Application


    IrDA

    • Infrared Developers Association

    • Laptop standard

      • Adaptec Airport

    • Data Rates

      • 9600 bps - 4 Mbps


    Universal serial bus
    Universal Serial Bus

    • USB - now the standard on most systems

    • 12Mbps capable (1.5Mbps in a lower speed)

    • Connects up to 127 devices

    • Hub/function architecture

    • Cable

      • special 4 wire cable Vcc, Ground, +/- data


    Ieee 1394
    IEEE-1394

    • Used by AppleCorp as Firewire

    • (note - although many in the industry have attributed the development of IEEE-1394 to Apple Corporation, this is not entirely true.)

    • Wiring - 6 wire copper connection (expect to become glass)


    Ieee 13941
    IEEE-1394

    • 100Mbps - with upgrades to 200Mbps and 400Mbps expected

    • Can (is) used to connect everything to a computer system - monitor, printer, hard disk drives, CDRoms, etc.


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