Ports, connectors, and cables

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Ports, connectors, and cables

• Ports
• A port is a connector into which you can plug
  cables from external devices, or in some cases in
  the devices themselves. there are two common port
  types , which are serial and parallel ports.
• Serial and Parallel Transmission
• Serial transmission is a technique in which bits
  of data are sent one at a time across the data
  transmission medium.
• Parallel Transmission is a technique in which one
  or more bytes is transmitted at a time.

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Serial transmission
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Parallel transmission
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Serial Ports

• Connectors into which you plug devices that use
  serial transmission to communicate with your pc.
• While there are many types of devices and ports
  that use serial transmission, when most people
  speak of serial ports they mean the
  communication oriented ports to which connect
  devices such as modems. They are called
  Communication or COM Ports
• Basic PC supports four COM Ports COM1, COM2,COM3
  and COM4
• Only two can be used at a time.
• Windows supports software emulation of additional
  ports--?Softmodems (winmodems) .

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Serial port resources
COM ports 1 and 3 and COM ports 2 and 4 share the
same IRQs. This means that you cant have COM
ports 1 and 3 (or 2 and 4) enabled At the same
time unless you reconfigure one of the ports to
use different IRQs.
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Serial port characteristics

• Port speed- The rate , in bits per second at
  which data communications proceed over the COM
  port. This speed controls how fast your computer
  interacts with the serial device, not that device
  s communications speed.
• Data bits The number of bits of data sent within
  a single block.
• Start/stop bits The number of bits added before
  and after the data to designate the beginning and
  end of the data within a block. Often this value
  is configured as just the stop bits.
• Parity Error checking method used over the COM
  port . Your choices include
• NoneParity checking disabled.
• EvenIf the sum of data bits is even number,
  the parity bit is set to 0. If the sum is odd
  the parity bit is set to 1. In this way the sum
  of data and parity bits is always an even
  number.
• Odd--- If the sum of data bits is an odd
  number , the parity bit is set to 0. If the sum
  is even the parity bit is set to 1. In this way
  the sum of data and parity is always an odd
  number.
• Mark--- The parity bit is always set to 1.
• Space--- The parity bit is always set to 0.

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Serial port characteristics contd

• Flow control is a means by which communication
  over a serial port can be slowed down or even
  stopped to permit the devices involved to keep
  pace with communications. Your choices include
• -NoneFlow control disabled.
• -Hardware---Devices use a separate flow control
  wire within the serial cable over which
  handshaking signals are sent. Through these
  signals devices can start and stop the
  communications.
• -Xon/Xoff--- A software hand shake technique in
  which transmit on (Xon) and transmit on (Xoff)
  signals are sent over the same data
  communications line as transmits data. The
  receiving device sends the Xon and Xoff signal to
  the sender. Xoff is ASCII character 19
  (equivalent to Control S key sequence) and Xon is
  ASCII 17 (Control Q).

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Male and female connectors (typical serial
connectors)
Male
Female
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Serial connectors
Pin 9
Pin 6
Pin 5
Pin 1
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Serial cables

• Multiple conductors
• At least two wires are required one for sending
  and one for receiving the other wires provide
  power, ground and control signal transmission.
• Send, receive, power, ground, etc.
• Two forms of serial cables
• Straight-through cable-- used to connect your PC
  to a serial device.
• Pin 1 goes to pin 1
• Pin 2 goes to pin 2
• Null modem cable
• Pins crossed and connected to simulate modem

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Pin numbers http//docs.hp.com/en/B2355-90137/apas
01.htmlNote DCE Short for Data Communications
Equipment, a device that communicates with a Data
Terminal Equipment (DTE) device in RS-232C
communications In practical terms, the DCE is
usually a modem and the DTE is the computer
itself .
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9-pin null modem connections
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25-pin null modem connections
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Parallel ports

• Parallel transmissions
• Often used for printers
• LPT (Line Printer) ports
• LPT1
• LPT2
• Additional ports through expansion adapters
• More modern PCs use USB

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Parallel port resources
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Port types

• Normal or Default (unidirectional)
• Bidirectional versions
• Standard Parallel Port (SPP)
• Enhanced Parallel Port (EPP)
• Extended capabilities port (ECP)
• Can use BIOS set up utility to modify modes
• Communications techniques
• For SPP the technique used is Compatibility or
  Centronics mode.
• EPP and ECC enable the PC to check the printers
  status before sending data. DMA and enhanced
  hand shaking protocols.

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Female 25-pin parallel port
Parallel port
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Centronics connectors
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PC input devices

• Keyboard
• Mouse
• Trackball
• Trackpad
• Pens (styli)
• Touch screens

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Keyboard port and connector
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AT keyboard port and connector
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Mouse port and connector
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Bar code reader with Y-cable