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EET 450 - Advanced Digital

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

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  1. EET 450 - Advanced Digital Chapter 21 Serial Ports

  2. Serial Communications • Contrasting with parallel communications - the individual bits are transmitted one at a time. • Uses time division multiplexing versus space division multiplexing

  3. Modern Serial • Options • classic - RS 232 • ACCESS.bus • IrDA optical • Universal Serial bus • P1394

  4. 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

  5. IrDA - optical serial version • 4 Mbps • no cable • 126 devices • USB - high speed serial • 12 Mbps • Special 4-wire cable • 127 devices

  6. IEEE 1394 - firewire • 100 Mbps • Special 6-wire cable • 16 devices per port

  7. 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

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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)

  17. 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.

  18. Chips • UART - Universal Asynchronous Receive r/Transmitter • 8250 • 16450 • 16550

  19. Access.bus • Allows 125 devices to a single port • Simple - Slow • Software flow control • Three layers • Physical • Base • Application

  20. IrDA • Infrared Developers Association • Laptop standard • Adaptec Airport • Data Rates • 9600 bps - 4 Mbps

  21. 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

  22. 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)

  23. 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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