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5 keyboard mouse_scanner



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  • Recall that COM 1 and COM 3 share IRQ 4 while COM 2 and COM 4 share IRQ 3- if the Mouse is using a COM port, the port on the same channel cannot be used
  • As we all know too well, today’s telephone lines are limited to 56Kbps transmission speed at best Know the signal abbreviations for certification


  • 1. Peripheral Devices
  • 2. Keyboards
    • Keyswitch Keyboards- employ an individual switch under each key- a plunger moves downward in response to a key press, making a connection between two signal lines coming from the keyboard controller
      • Inexpensive
      • Simple to make
      • Simple to service
      • Bounce led to duplicate letters, but decreased tension leads to finger fatigue
      • Bulky
      • Require Voltage to operate
    • Second effort employed an electric controller to constantly scan for keystrokes, ignoring those which are not present for a second scan
  • 3. Capacitive Keyboards
    • Placed two sheets of semi-conductive materials separated by a thin sheet of Mylar inside the keyboard- a key press creates contact between the sheets changing the capacitance- the controller is aware of which key is pressed by reading a scan code
      • You cannot repair capacitive switch keyboards
      • Durable
      • Inexpensive
  • 4. Keyboard Connectors
    • DIN 5- standard on the IBM PC or XT/AT form factor machines
    • Mini- PS/2- smaller then the DIN 5- so named because it was initially introduced on the IBM PS/2
  • 5. Cleaning Keyboards
    • Remove it from the computer and soak it in distilled, demineralized water as soon as a spill occurs
      • A dry spill is much harder to clean
      • Running keyboard through the dishwasher is not recommended
      • Be sure the keyboard is completely dry before reconnecting it and using it
    • Disassemble and use a special keyboard cleaner
      • Due to the amount of time this method requires, it is cheaper to simply buy a new keyboard
  • 6. The Mouse
    • GUI - Graphical User Interface- the use of pictures to represent computer entities or basic commands (i.e.- save, exit)
    • Mouse - a device specifically designed to interact with the pictures represented in a GUI interface- translates moves on a horizontal surface into movements of a pointer on the screen
  • 7. Types of Mice
    • Opto-mechanical- contains a round ball that makes contact with two internal rollers representing the x and y axis respectively- optical sensors interpret light patterns as speed and direction of movement and send those to the mouse control software on the computer
    • An Optical Mouse has no ball- rather it uses a special mouse pad and a beam of laser light- the pad reflects the laser back to a sensor in the mouse that detects movement and direction
      • Will not work without the special mouse pad
  • 8. Mouse Interfaces
    • Serial – the first major mouse interface was a DB9 serial
      • Major disadvantage was the use of a COM port
    • Bus Interface- an expansion card with a PS/2 connector
      • Did not take up a COM port, but it does use an interrupt
    • PS/2 Mouse Interface - the same PS/2 connector integrated on the motherboard
  • 9. Cleaning the Mouse
    • 1. Turn the mouse upside down and remove the ball by rotating the retaining ring
    • 2. Flip the mouse upright so the ball will fall out
    • 3. Use a small eyeglass screwdriver to remove the circular accumulation of dust and dirt on the rollers
    • 4. If needed, soak in isopropyl alcohol to loosen
    • 5. Reassemble
  • 10. Other Pointing Devices
    • Trackballs - essentially an upside-down mouse- the ball moves while the casing is stationary- typical trackballs are large desktop style- portable trackballs are more compact and may be held in the hand
    • Drawing Tablets - a sheet of plastic with a rubberized coating on which a user my use a stylus to “draw” images
      • Electromagnetic Tablets- tablet has a grid of wires across which an electrical pulse is sent at regular intervals- a sensor in the stylus translates the signals to x and y coordinates
      • Resistive Tablets - have a resistive surface under the rubberized coating that induces variable current at different spots on the x and y axis translating to specific coordinates
      • Acoustic Tablets - stylus has a small spark which activates at the press of a button- microphones on the x and y axis translate the coordinates into values for the computer
    • Touch Screens- a screen which is sensitive to touch
      • Optical - the physical touch breaks a beam of light emanating from the screen to determine x and y coordinates
      • Capacitive screens- like the keyboards, employ two sheets of clear plastic separated by a layer of air- touching a particular spot changes the total capacitance and translates to an x, y coordinate
  • 11. Scanners
    • Flatbed Scanners - resemble the top half of a photocopier- they employ a charge coupled device, a motorized carriage, and a light source to convert images in to computerized files
      • Usually SCSI
      • Can be manufacturer proprietary
    • Handheld Scanners - contain all the same components in a smaller enclosure with wheels
      • Inexpensive
      • Decent Capabilities
      • Slow
      • Quality Depends Largely on User
      • Scanners may be cleaned carefully with glass cleaner
  • 12. Modems
    • Modem actually stands for Modulator/Demodulator- digital signals can lose strength over long distances- analog signals may get weaker, but the sound does not degrade- therefore, analog signals are a better choice for communication over a telephone line. The modem translates the digital signals from the computer to analog signals for transmission and visa versa
      • Modem Signal Abbreviations
      • OH- Off the Hook
      • SD(TX) Transmit Data
      • RD(RX) Receive Data
      • AA Auto Answer