EET 450 - Advanced Digital Chapter 21 Serial Ports.

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.