eet 450 - advanced digital chapter 21 serial ports
Post on 21-Dec-2015
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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 ACCESS.bus IrDA optical Universal Serial bus P1394
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
IrDA - optical serial version 4 Mbps no cable 126 devices
USB - high speed serial 12 Mbps Special 4-wire cable 127 devices
IEEE 1394 - firewire 100 Mbps Special 6-wire cable 16 devices per port
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 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 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 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
The traditional COM portPort speeds are restricted by internal clock of PC 150:300:600:1200:2400:4800:960019200:38400:57600:115200physical connection Standard connectors
DB25 DB9
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-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-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
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
designed to run on unshielded twisted pair (UTP)Shielded cable can extend effective rangeWiring depends on flow control Software - 3 wires needed
(XMIT/RCV/Ground) Hardware - all wires as above
Connectors - DB25 or DB9 (m/f)
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
UART - Universal Asynchronous Receive r/Transmitter82501645016550
Access.bus
Allows 125 devices to a single portSimple - SlowSoftware flow controlThree layers Physical Base Application
IrDA
Infrared Developers AssociationLaptop standard Adaptec Airport
Data Rates 9600 bps - 4 Mbps
Universal Serial Bus
USB - now the standard on most systems12Mbps capable (1.5Mbps in a lower speed)Connects up to 127 devices Hub/function architectureCable special 4 wire cable Vcc, Ground, +/-
data
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-1394
100Mbps - with upgrades to 200Mbps and 400Mbps expectedCan (is) used to connect everything to a computer system - monitor, printer, hard disk drives, CDRoms, etc.