S.N.COLLEGE, GADHINGLAJKeyboard• The keyboard is a peripheral device which is directly connected on to the motherboard (system board).• The keyboard is basically a set of switches (much like a typewriter)• Switches are connected in the form of a matrix, surrounded by electronic circuits• This Circuits monitor the key matrix that continuously scans the keys to recognize key action and generate a scan code.
S.N.COLLEGE, GADHINGLAJKey Boards Types• Serial keyboard• Parallel keyboard• Serial Keyboard –It is a keyboard which outputs the data in serial form, i.e. bit by bit. –The computer converts serial data into parallel 8-bit data. –They use only single line to transmit the data.
S.N.COLLEGE, GADHINGLAJ Parallel Keyboard• It is a keyboard which outputs all the 8-bits at a time in a parallel form.• All the bits are sent simultaneously on different lines.• In this the transmission is faster, needs a thicker cable with more number of wires.• In PCs we always use serial keyboards.
S.N.COLLEGE, GADHINGLAJBoard Switches• Different types of key switches.• Mechanical key switches• Membrane key switches• Capacitive key switches• Hall effect key switches• Reed Relay key switches
S.N.COLLEGE, GADHINGLAJFunctioning of the Keyboard• The processor in the original PC keyboard was an Intel 8048 micro-controller chip• Newer keyboards often use an 8049 version that has own RAM, built in ROM or other micro-controller chips compatible with the 8048 and 8049.• In an AT-type keyboard design, the keyboard serial interface is connected to a special keyboard controller on the motherboard(Intel 8042).
S.N.COLLEGE, GADHINGLAJFunctioning of the Keyboard• When a switch is pressed, a processor in the keyboard itself identifies which key is pressed by identifying which grid location in the matrix shows continuity.• The keyboard processor also interprets how long the key is pressed and can even handle multiple keystrokes at the same time
S.N.COLLEGE, GADHINGLAJ Functioning of the Keyboard• When you press a key, in most cases the contact actually bounces slightly .• The processor in the keyboard is designed to filter this or debouncethe keystroke.• The keyboard processor must distinguish bounce from a double key strike actually intended by the keyboard operator.
S.N.COLLEGE, GADHINGLAJ Functioning of the Keyboard• Universal Peripheral Interface (UPI) slave micro controller chipis also available in the original AT design• It has its own 2K of ROM and 128 bytes of RAM.• Some systems may use the 8041 or 8741 chips, which differ only in the amount of built-in ROM or RAM• Other systems now have the keyboard controller built into the main system chipset.
S.N.COLLEGE, GADHINGLAJMembrane switches• Very similar in operation to rubber dome keyboards.• A membrane keyboard does not have separate keys .• In this keyboard, two rubber or plastic sheet are used as row conductor sheet and column conductor sheet.• When the key top is pressed, it forces the row conductor sheet through the hole to touch the column conductor sheet.
S.N.COLLEGE, GADHINGLAJ Membrane switches• These row and column lines are made on the plastic or single rubber sheet• It uses silver or some other conductor ink for each row and column of keys with bulges for each key on the keyboard.• This keyboard can be made very thin, as a completely sealed unit.
S.N.COLLEGE, GADHINGLAJ TypematicFunctions• If a key on the keyboards is held down, it becomes typematic, which means that the keyboard repeatedly sends the key press code to the motherboard.• In AT-style keyboards, typematic rate is adjustable by sending the keyboard processor the appropriate commands.
S.N.COLLEGE, GADHINGLAJKeyboard Interface• Interface between the keyboard cable and the system unit is the keyboard interface which is a DIN (or mini-DIN if its a PS/2) plug that has five (or six, for mini-DIN) pins as shown.• All together there are four lines (wires) used for interfacing the keyboard with the system motherboard. They are – Keyboard data (KBDATA) – Keyboard clock (KBCLK) – DC source (+5V VCC) –DC ground (0V GND)
S.N.COLLEGE, GADHINGLAJ Keyboard Interface• Universal Serial Bus (USB) interface is becoming more popular for keyboards, and some models may, in fact, require you to use a USB port unless you have a USB-to-PS/2 adapter to make the USB keyboard compatible with the PS/2 keyboard port.• A USB connection is faster than the other, older I/O ports on your computer, such as COM and parallel ports.
S.N.COLLEGE, GADHINGLAJCommon Keyboards Types• The most common keyboards are:• 101-key Enhanced keyboard• 104-key Windows keyboard• 83-key PC and XT keyboard (Obsolete)• 84-key AT keyboard (Obsolete)
S.N.COLLEGE, GADHINGLAJ Enhanced 101-Key (or 102-Key) Keyboard • In 1986, IBM introduced the "corporate" Enhanced 101-key keyboard for the newer XT and AT models. • IBM 101-key units originally came in versions with and without the status-indicator LEDs, depending on whether the unit was sold with an XT or AT system. • With the replacement of the Baby-AT motherboard and its five-pin DIN (an acronym for Deutsche Industries Norm) keyboard connector by ATX motherboards, which use the six-pin mini-DIN keyboard connector, virtually all keyboards on the market today come with cables for the six-pin mini-DIN connector introduced on the IBM PS/2s.
S.N.COLLEGE, GADHINGLAJEnhanced 101-Key (or 102-Key) Keyboard• 101-key keyboard layout can be divided into the following four sections: –Typing area –Numeric keypad –Cursor and screen controls –Function keys
S.N.COLLEGE, GADHINGLAJ104-Key (Windows 9x/Me/2000) Keyboard• When Microsoft released Windows 95, it also introduced the Microsoft Natural Keyboard, which implemented a revised keyboard specification that added three new Windows-specific keys to the keyboard.• 104-key layout includes left and right Windows keys and an Application key which are used for operating system and application-level keyboard combinations, similar to the existing Ctrl and Alt combinations.
S.N.COLLEGE, GADHINGLAJ104-Key (Windows 9x/Me/2000) Keyboard• Windows keyboard layout calls for the Left and Right Windows keys (called WIN keys) to flank the Alt keys on each side of the spacebar, as well as an Application key on the right of the Right Windows key.• WIN keys open the Windows Start menu, which you can then navigate with the cursor keys.• Application key simulates the right mouse button which in most applications, it brings up a context sensitive pop-up menu.
S.N.COLLEGE, GADHINGLAJWindows 9x/Me/2000 key combinations used
S.N.COLLEGE, GADHINGLAJ Cordless Keyboards• These are like regular keyboards, except instead of having a keyboard cable that runs from the keyboard to the PC, they have no cord.• Wired interface between the keyboard and the motherboard is replaced with a wireless one.• They also typically cost more than the corded models.
S.N.COLLEGE, GADHINGLAJMultimedia and Web-Enabled Keyboards• Many keyboards feature fixed-purpose or programmable hotkeys that can launch Web browsers, run the Microsoft Media Player, adjust the volume on the speakers, change tracks on the CD player, and so forth.• Operating Systems such as Windows 98, Windows Me and Windows2000 support these keyboards to use their hot keys.
S.N.COLLEGE, GADHINGLAJMultimedia and Web-Enabled Keyboards
S.N.COLLEGE, GADHINGLAJErgonomic Keyboards• A trend that began in the late 1990s is to change the shape of the keyboard instead of altering the character layout which has resulted in a number of so-called ergonomic designs.• Most common of these designs splits the keyboard in the centre, bending the sides outward.