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INPUT/OUTPUT DEVICES. Without reference, identify principles relating to I/O Devices with at least 70 percent accuracy. . INPUT/OUTPUT DEVICES.
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INPUT/OUTPUT DEVICES Without reference, identify principles relating to I/O Devices with at least 70 percent accuracy.
INPUT/OUTPUT DEVICES • Keyboards – All keyboards have four basic types of keys grouped together; they are the typing keys, numeric keypad, function keys, and control keys. They can be connected to the PC by a 5-pin DIN connector, 6-pin IBM PS/2 connector, or by a USB connector. • Keyboards have a small microprocessor built into them with a keyboard controller that communicates with the main microprocessor located on the computer’s motherboard. The keyboard’s microprocessor continually checks the key matrix to see if any change has occurred in the key position – has it been depressed or released. Each key is assigned two scan codes, one to indicate the key was depressed (make code) and the other to indicate the key was released (break code). When make or break codes are detected for a key, the keyboard microprocessor identifies which key was activated, and the scan code is converted to 16-bit serial data and sent to the PC’s microprocessor.
INPUT/OUTPUT DEVICES • The use of two codes (make and break) for each key allows the microprocessor to determine how long a key is depressed. This enables it to see operations like holding the shift key while depressing a letter key to produce an upper case letter. To ensure the system is not fooled by noise called bounce, a key activation must be detected on two subsequent scans by the microprocessor. Typically, the microprocessor checks for key actions every few microseconds. The PC receives keyboard scan codes from the keyboard microprocessor at a special I/O port. A keyboard controller chip tells the computer microprocessor that a scan code is available by issuing an interrupt signal. The computer’s microprocessor sorts through a list of scan codes, which are part of the computer system BIOS, to determine which key is pressed.
INPUT/OUTPUT DEVICES • Keyboards have a sound and feel when you press the keys; this feel gives the user a sense of response while typing. The trend is to have a keyboard that fives an audible click when the keys are pressed and the keys feel firm and spring back into position rapidly. • Mouse • The mouse serves two functions; cursor movement and function selection (often called “point and click”). The mouse is rolled around on a flat surface, creating corresponding movement of the cursor on the monitor screen. The cursor can be moved in any direction, the limits being the boundaries of the screen. Let’s say we moved the courser to a spot on the computer that has the function “print.” The flashing cursor would be on the “print” choice – this is known as “pointing.” The second function involves the use of buttons on the mouse. Once the cursor is positioned over some area on the screen which equates to a function, in our case “print,” a button on the mouse is pressed, called clicking, to select and activate the function.
INPUT/OUTPUT DEVICES • Monitors: • Cathode ray tube, or CRT - is the oldest electronic image-generating system. This device is based on a special form of a vacuum tube, a glass bottle that has been completely evacuated then filled with inert gas. Internal to this tube is a cathode that shoots a beam of electrons toward a positively charges anode. Because the cathode works like a gun, it is often called an electron gun. The electrons that are fired towards the anode never really strike it; they speed by quickly and strike a phosphor face. The phosphor glows when struck with the electrons. If left like that they will continually strike the same spot. A yoke, or electromagnetic field, is placed around the tube and it bends the electron beam during its flight. The magnetic field is carefully controlled so that the beam scans each individual display line down the face of the tube.
INPUT/OUTPUT DEVICES • The sweep of the beam is from the upper left corner of the screen to the lower right corner. A complete sweep of the screen is called a field. Upon completing a field, the beam returns to the upper left corner to beg in a new field. Depending on your display adapter (video card) the screen can be refreshed or redrawn 60, 72, 75 or 85 times per second or hertz. When an adapter scans only every other line of the field, it is known as noninterlacing. This allows for the use of less expensive components. Another method is known as interlacing. That is where every other line of a field is scanned and then on the second pass, the previously unscanned lines are scanned, this interlacing the fields.. This method provides a flicker-free monitor; this the principle behind a television.
INPUT/OUTPUT DEVICES • Display – The type of display that you usually see as an integral part of a medial device is called a liquid crystal display or LCD. LCDs are low power devices that block light. To make patterns visible, they selectively block either reflected light (reflective LCDs) or the light generated by a secondary source, located behind, above, or on the side of the LCD panel (backlit LCDs). A basic LCD display is constructed from back to front and includes a: • Polarizing filter • Sheet of micro-grooved glass • Electrode • Alignment layer • Liquid crystal in a state called the nematic phase • Alignment layer • Electrode • Sheet of micro-grooved glass • Polarizing filter 90 degrees offset from first filter
INPUT/OUTPUT DEVICES • LCDs have two ways in which current is applied to the molecules: passive matrix and active matrix. A passive matrix has a grid of horizontal and vertical conductors, and each pixel is at the intersection of these conductors. The pixel is darkened by sending current through the conductors to the liquid crystal. This method has a slow response time and has poor contrast. The viewing angle of a passive matrix screen is limited to about 45 degrees from the center of the LCD. • The active matrix, or thin film transistor (TFT), places a transistor at every pixel. The transistor acts as a relay. A small current is sent to it through the horizontal and vertical grid, and in response, the transistor switches on a much higher current to activate the LCD pixel. The advantage of the active matrix design is that a smaller current needs to traverse the grid so that the pixel can be switched on and off faster. The brightness and contrast are much better, and the viewing angle is close to 100 degrees form the center of the LCD screen.
INPUT/OUTPUT DEVICES • Touch screen – Touch screen technology requires a touch screen panel, a microprocessor-based controller, and software that communicates with the main microprocessor on the motherboard. • Resistive – This technology has three layers, the first layer is a glass panel and the second layer is a thin metallic layer of resistive and conductive material. There are ultra-thin spacers in between the layers to prevent them from touching. The third layer is a scratch resistant layer used to protect the second layer. An electrical current runs through the glass panel and the metallic layer. When you touch the screen the controller senses a change in the resistance and capacitance, calculates the exact location of the touch, and then sends it to the display by way of the microprocessor. If you touched a function on the front panel then that function would activate.
INPUT/OUTPUT DEVICES • Surface wave – This technology is the most advanced; it uses ultrasonic waves on the touch screen. There are transducers for sending ultrasonic waves (send transducers) placed on the top (X-axis) and the left side (Y-axis). The corresponding transducers used for receiving the ultrasonic waves (receive transducers) are placed on the opposite sides. When you make contact with the screen, some of the ultrasonic waves are absorbed by your finger or a rubber-tipped probe. This reduction in ultrasonic waves is detected as a touch. The controller senses a change in the ultrasound waves, calculates the exact location of the touch, and then sends it to the display by way of the microprocessor.
INPUT/OUTPUT DEVICES • Capacitive – This type of touch screen is covered with a layer that stores a capacitive charge. When you touch the screen a small amount of charge is concentrated at that point. Sensors located in each corner make measurements of the change, the controller calculates the coordinates of the contract and it is forwarded to the software for action. This type of touch screen doesn’t work well in a medical environment. • Infrared – This technology uses infrared LED transmitters on the X-axis and Y-axis of the touch screen; the LED receivers are located opposite of the transmitters. For this type of screen, you don’t have to physically touch the screen to get a response, just break the light beam. It works well with any type of device that can be placed into the beam whether it is gloved finger, or a screwdriver. If the touch screen is scratched or damaged in any way, it will not hinder the operation of the touch screen.
INPUT/OUTPUT DEVICES • Printers – Printer technology is broken down into two major categories; impact and non-impact. • Impact printers are broken into two basic types of printers: dot matrix and character; do to their outdated technology we will not discuss these. • Non-impact printers: • Ink jet – This type of printer uses either black or color ink-filled print cartridge(s) attached to the side of the ink jest’s print head. The print head is made up of 300 to 600 ink-filled chambers, each attached to a nozzle. These nozzles are between 50-60 microns in diameter, smaller than a human hair. The print head stepper motor uses a belt drive to move the print head/cartridge assembly sideways across the width of a sheet of paper that is fed through the printer without touching the print head. The paper path starts at the paper feeder; rollers grip the bottom of the page and pull the paper from the feeder under the print head. The page feed stepper motor drives the roller in coordination with the print head stepper motor, so that when a line has finished printing the next line becomes available.
INPUT/OUTPUT DEVICES • The printer has its own internal circuit board to control its various functions. Ink jet printers are commonly available with parallel port connections as well as USB. The SCSI interface is also available, but is not as popular • Laser – laser printers are used extensively with medical equipment, especially in the imaging department. The laser printer presents the best quality print of all the printers discussed here.
INPUT/OUTPUT DEVICES • To create a letter/image quality output, the printer must control five different operations simultaneously: • It must interpret the signals coming from the computer • Translate those signals into instructions that control the movement of the laser beam • Control the movement of the paper • Sensitize the paper so that it will accept the black toner that makes up the image • Fuse that image to the paper • The PC’s operating system sends signals to the laser printer to determine where each dot of printing toner is to be placed on the paper. The instructions from the printer’s processor rapidly turn on and off a beam of light from a class one laser. A spinning mirror deflects the laser beam so that the path of the beam is a horizontal line across the surface of a cylinder called the drum.
INPUT/OUTPUT DEVICES The combination of the laser beam being turned on and off, and the movement of the beam's path across the drum, results in many tiny points of light hitting a line across the surface of the drum. When the laser finishes flashing points of light across the entire width of the drum, the drum rotates, usually 1/300th of an inch in most laser printers, and the laser beam begins working on the next line of dots. • Simultaneously as the drum begins to rotate, a series of gears and rollers feeds a sheet op paper into the print engine along a path called the paper feed. The paper feed pulls the paper past an electrically charged wire called the corona wire, which give the paper a static electrical charge. The charge may be either positive or negative, depending on the design of the printer. For this example, we’ll assume that the charge is positive.
INPUT/OUTPUT DEVICES • Each pint of light that strikes the drum, causes a negatively charged film, usually made of zinc oxide and other materials, on the surface of the drum to change its charge so that the dots have the same electrical charge as the sheet of paper (for our example, the light would change the charge from negative to positive). Each positive charge marks a dot that will eventually print black on the paper. The areas of the drum that remain untouched by the laser beam retain their negative charge to correspond with the white areas on the paper. • About halfway through the drum’s rotation, the drum uses a bin that contains a black power called toner. The toner has a negative electrical charge, the opposite of the charges created on the drum by the laser beam. Because particles with opposite static charges attract each other, toner sticks to the drum in a pattern of small dots wherever the same as the charge on the drum and onto the paper. Finally, the paper is fed under a heated roller that bonds the toner to the paper.
