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Parallel port – signals and timing diagram – IEEE1284 modes – asynchronous communication – serial port signals – video adapters – graphic accelerators – 3D graphics accelerator issues – DirectX – mice – modems – keyboards – sound boards – audio bench marks.

sound boards

l Have ports for external stereo speakers and microphone input

l May be Sound-blaster compatible

l Sampling accuracy is critical to performance

l Stages of computerized sound

u Convert from analog to digital (digitize)

u Store digital data in compressed data file

u Reproduce or synthesize sound (digital to analog)

Installing a Sound Card

l Process

u Physically install card in empty PCI slot on the motherboard

u Install sound card driver

u Install sound applications software

l Special considerations for Windows 2000/XP installations


  • User presses or releases button
  • Buttons read by on-board Intel 8048 Microcontroller
    • Microcontroller De-bounces buttons
    • Generates scan code(s)
    • Prefixes extended keys with 224 (EOh)
  • Microcontroller serially transmits Scan codes at 10,000 baud to parallel latch on motherboard
    • IRQ1 Triggered when complete byte arrives.
    • Data available at Port 60h
    • Acknowledge Keyboard: (toggle bit 7 of port 61h)
      (See Lab manual for details)
  • INT9 Called to process keystroke (usually BIOS)
    • Default BIOS routine tracks [shirft], [alt], [ctrl], [CapLock], [NumLock] status word
    • Keyboard buffer holds keystrokes until read by INT16 (KBDIN)

Keyboard Switches

Keyboards use a variety of switch technologies.

Capacitive switches are considered to be non-mechanical because they do not physically complete a circuit like most other keyboard technologies.

Instead, current constantly flows through all parts of the key matrix. Each key is spring-loaded and has a tiny plate attached to the bottom of it.

When you press a key, it moves this plate closer to the plate below it. As the two plates move closer together,

the amount of current is flowing through the matrix changes.

The processor detects the change and interprets it as a key press for that location.

Capacitive switch keyboards are expensive, but they have a longer life than any other keyboard. Also, they do not have problems with bounce since the two surfaces never come into actual contact.

All of the other types of switches used in keyboards are mechanical in nature. Each provides a different level of audible and tactile response — the sounds and sensations that typing creates. Mechanical key switches include:

* Rubber dome

* Membrane

* Metal contact

* Foam element

A parallel port is a type of interface found on computers (personal and otherwise) for connecting various peripherals.

It is also known as a printer port or Centronics port. The IEEE 1284 standard defines the bi-directional version of the port.

Parallel Interface

  • Originally Designed for printers
  • Provides 8-bit I/O
  • Attaches via 25-pin or Centrontics connector
  • Provides TTL-level (5V) external I/O
  • Major Signals






Byte-wide data bus


To device

Write signal


From device

Don’t send more data


From device

Acknowledge (interrupt signal)


To device

Initialize external device

Out of Paper

From device

Status signal


  • Writing to the parallel port

IEEE 1284 is a standard that defines bi-directional parallel communications between computers and other devices.

In the 1970s, Centronics developed the now familiar printer parallel interface that soon became a de facto standard.

The standard became non-standard as enhanced versions of the interface were developed, such as the HP Bitronics implementation released in 1992.

In 1991 the Network Printing Alliance was formed to develop a new standard. In March 1994, the IEEE 1284 specification was released.

The IEEE 1284 standard allows for faster throughput and bidirectional data flow with a theoretical maximum throughput of 4 megabits per second, with actual throughput around 2 megabits, depending on hardware.

In the printer venue, this allows for faster printing and back-channel status and management.

Since the new standard allowed the peripheral to send large amounts of data back to the host, devices that had previously used SCSI interfaces could be produced at a much lower cost. This included scanners, tape drives, hard disks,

computer networks connected directly via parallel interface, network adapters and other devices.

No longer was the consumer required to purchase an expensive SCSI card—they could simply use their built-in parallel interface.

These low-cost devices provided a platform to leapfrog the faster USB interface into its present popularity, displacing the parallel devices.

However, the parallel interface remains highly popular in the printer industry, with displacement by USB only in consumer models.

Transfer mode

Distance (metre)
(AB cable)/(CC-cable)[2]

Speed (bits per second) [3]

Compatibility (SPP)















IEEE 1284 standards

  • IEEE 1284-1994: Standard Signaling Method for a Bi-directional Parallel Peripheral Interface for Personal Computers
  • IEEE 1284.1-1997: Transport Independent Printer/System Interface- a protocol for returning printer configuration and status
  • IEEE 1284.2: Standard for Test, Measurement and Conformance to IEEE 1284 (not approved)
  • IEEE 1284.3-2000: Interface and Protocol Extensions to IEEE 1284-Compliant Peripherals and Host Adapters- a protocol to allow sharing of the parallel port by multiple peripherals (daisy chaining)
  • IEEE 1284.4-2000: Data Delivery and Logical Channels for IEEE 1284 Interfaces- allows a device to carry on multiple, concurrent exchanges of data

The IEEE 1284 standard was approved in march 1994 as the Standard Signaling Method for a Bidirectional Parallel Peripheral Interface for Personal Computers. And is the first approved standard for parallel transmission on PCs. The idea was to create a standard that was backward compatible with the old Centronics standard. With the new standard higher speeds and greater distances are possible plus there is the capability also sending to the host (bidirectional).

The maximum speed that is allow over the new parallel bus is 2 MBps (16 Mbps). The cable length is determend by the mode that is used. Within the IEEE 1284 there are 5 different modes defined:

Compatibility mode
This one is compatible with all previous version of the parallel port. Data rates are possible up to 150 bytes per second @ 6 meter (20 ft) with an AB-cable or up to 150 kbps @ 10 meter (32.8 ft) with a CC-cable.

Nibble mode
This is a uni-directional interface. Only data transfers from periperal to host are possible. Data is send from the e.g. printer to the PC in a nibbles (4 bits). Combined with the Compatibility mode this is what Hewlett Packard calls “Bi-tronics”.
For the Nibble-mode speeds of up to 50 kbps @ 6 meter (20 t) are possible. With a CC-cable this can be increased to up to 150 kbps @ 10 meter (32.6 ft).

Byte mode
Byte mode makes it possible to send data from the peripheral to the host in bytes (8 bits). Combined with the Compatibility mode you have a “Bidirectional port”.
Speeds are possible up to 500 kbps @ 10 meter (32.8 ft) when CC-cables are used.

EPP mode
This is a mode in which data can be transfered from host to peripheral or vice versa, but not at the same time, so this is a half-duplex connection (mostly used by CD-ROMs, tape-drives, harddisks).
Speeds can range from 500 kbps to up to 2 Mbps @ 6 meter (20 ft) or 10 meter (32.8 ft) when CC-cables are used.

ECP mode
This is a mode in which data can be transfered from host to peripheral or vice versa, but not at the same time, so this is a half-duplex connection (mostly used by printers and scanners).
Speeds can range from 500 kbps to up to 1 Mbps @ 6 meter (20 ft) or 10 meter (32.8 ft) when CC-cables are used.

Every device can only be in one mode at a time. So the IEEE 1284 workgroup invented a way of determining which mode should be used with which device, that is called Negotiation. The Negotiation part doesn’t affect older devices, but IEEE 1284 compliant devices can tell the host what they are and which mode to use.

Cables and Connectors
The IEEE defined three types of connectors and six types of cables. The type A connector is the parallel port connector (Sub-D25) found on most computers. The type B connector is what is usually called the Centronics connector. And there is a new connector that is called MDR36 and which is called type C. The pinning for the Centronics and Sub-D25 is not changed.
The different cables that are defined are:


Type A male to type A male


Type A male to type A female


Type A male to type B


Type A male to type C


Type B male to type C


Type C male to type C

Also the cable characteristics are defined:

  • The cable shield must be connected to the connector back shell using a 360° concentric method
  • The shield must be minimal 85 % optical braid coverage over foil
  • The maximum crosstalk is not greater then 10 %
  • All signals are send over a twisted pair with their signal ground return
  • Each pair must have an impedance of 62 ± 6 ohms @ 4 to 16 MHz

Asynchronous communication

  • One definition of asynchronous: transmitter and receiver do not explicitly coordinate each data transmission
    • Transmitter can wait arbitrarily long between transmissions
    • Used, for example, when transmitter such as a keyboard may not always have data ready to send
  • Asynchronous may also mean no explicit information about where data bits begin and end

Modem: (MODulator-DEModulator). The modem is simple in principle but complex in design.

It is used to transmit data over physically remote locations over traditional telephone lines. Unfortunately, phone lines cannot carry digital data: they are meant to carry sounds (analogue data). When sending data, the computer sends digital data to the modem.

The modem converts the digital 1’s and 0’s to sounds (e.g. High pitched sound for a one. Low pitched sound for a zero). This explains the “shushhhhhhhhhing” noise your modem makes when you connect to the internet: that noise is thousands of ones and zeroes being pumped down the phone line each second.

Converting digital data to sound is called modulation. The sound travels as noise over the phone line until it reaches the modem at the other end of the line. Because the other modem is in receiving mode, it listens to the sounds and converts the high and low pitched sounds back to ones and zeros (demodulation) and passing them to the computer. When the second computer wants to transmit, it switches from demodulation (listening) to modulation (talking), and sends data-sounds to the first modem which is now listening.

Modems are rated by speed: a 56K modem can transmit (a theoretical maximum of) about 56,000 ones and zeros per second.
Important note 1: the “K” in “56K” refers to BITS, not BYTES. While a 56K file on
disk means “56 kilobytes” (56,000 bytes), “56K” in modems means “56 kiloBITS” which is roughly 5.6 kiloBYTES. Many people do not realise this. Amaze your friends at your next party with this pearl of wisdom.
Important note 2: 56K modems receive at 56K but can only transmit at 33.6K.

The problem with phone lines is that they were never designed to transmit 56,000 sounds per second with perfect accuracy. They were designed for grandma to chat to mum about scones. An occasional click or bit of static on the line does not bother granny but it can destroy entire computer conversations. If only one bit out of 70,000,000 is wrong, your entire downloaded file can be ruined.

Internal modems (that plug into an expansion slot inside the computer) have less intelligence and rely on the CPU to do a lot of their work – as do USB modems. External modems (that plug into a serial port) do all their work themselves and put less strain on the CPU.

video adapters

  • The video adapter’s job is to store an in-memory representation of the currently displayed image on the video monitor. The adapter converts this representation to a signal understood by the monitor.
  • This in-memory representation of the display consists of a 2-dimensional matrix of dots, called pixels (for Picture Elements). The dimensions of this matrix can vary depending upon the characteristics of the video adapter and the monitor; the larger the matrix, the more detail can be displayed onscreen at any time.
  • Video adapters are equipped with their own RAM chips to store these matrices. Adapters with more memory can represent higher resolutions and/or numbers of colours, than can comparable adapters with less memory.

A video adapter (alternate terms include graphics card, display adapter, video card, video board and almost any combination of the words in these terms) is an integrated circuit card in a computer or, in some cases, a monitor that provides digital-to-analog conversion, video RAM, and a video controller so that data can be sent to a computer’s display. Today, almost all displays and video adapters adhere to a common denominator de facto standard, Video Graphics Array (VGA). VGA describes how data – essentially red, green, blue data streams – is passed between the computer and the display. It also describes the frame refresh rates in hertz. It also specifies the number and width of horizontal lines, which essentially amounts to specifying the resolution of the pixels that are created. VGA supports four different resolution settings and two related image refresh rates.

In addition to VGA, most displays today adhere to one or more standards set by the Video Electronics Standards Association (VESA). VESA defines how software can determine what capabilities a display has. It also identifies resolutions setting beyond those of VGA. These resolutions include 800 by 600, 1024 by 768, 1280 by 1024, and 1600 by 1200 pixels.

A board that plugs into a personal computer to give it display capabilities. The display capabilities of a computer, however, depend on both the logical circuitry (provided in the video adapter) and the display monitor. A monochrome monitor, for example, cannot display colors no matter how powerful the video adapter.

Many different types of video adapters are available for PCs. Most conform to one of the video standards defined by IBM or VESA.

Each adapter offers several different video modes. The two basic categories of video modes are text and graphics. In text mode, a monitor can display only ASCII characters. In graphics mode, a monitor can display any bit-mapped image. Within the text and graphics modes, some monitors also offer a choice of resolutions. At lower resolutions a monitor can display more colors.

Modern video adapters contain memory, so that the computer’s RAM is not used for storing displays. In addition, most adapters have their own graphics coprocessor for performing graphics calculations. These adapters are often called graphics accelerators.

Video adapters are also called video cards, video boards, video display boards, graphics cards and graphics adapters.

Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay, DirectSound, and so forth. DirectX, then, was the generic term for all of these APIs and became the name of the collection. After the introduction of the Xbox, Microsoft has also released multiplatform game development APIs such as XInput, which are designed to supplement or replace individual DirectX components.

Direct3D (the 3D graphics API within DirectX) is widely used in the development of computer games for Microsoft Windows, Microsoft Xbox, and Microsoft Xbox 360. Direct3D is also used by other software applications for visualization and graphics tasks. In CAD/CAM engineering, for instance, it rivals the OpenGL by its ability to quickly render 3D graphics on DirectX-compatible graphics hardware. As Direct3D is the most widely publicized component of DirectX, it is common to see the names “DirectX” and “Direct3D” used interchangeably.

The DirectX software development kit (SDK) consists of runtime libraries in redistributable binary form, along with accompanying documentation and headers for use in coding. Originally, the runtimes were only installed by games or explicitly by the user. Windows 95 did not launch with DirectX, but DirectX was included with Windows 95 OEM Service Release 2.[1] Windows 98 and Windows NT 4.0 both shipped with DirectX, as has every version of Windows released since. The SDK is available as a free download. While the runtimes are proprietary, closed-source software, source code is provided for most of the SDK samples.

The latest versions of Direct3D, namely, Direct3D 10 and Direct3D 9Ex, are only officially available for Windows Vista, because each of these new versions were built to depend upon the new Windows Display Driver Model that was introduced for Windows Vista. The new Vista/WDDM graphics architecture includes a new video memory manager that supports virtualizing graphics hardware to multiple applications and services such as the Desktop Window Manager

In computing, a mouse (plural mice, mouse devices, or mouses) is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of a small case, held under one of the user’s hands, with one or more buttons. It sometimes features other elements, such as “wheels”, which allow the user to perform various system-dependent operations, or extra buttons or features can add more control or dimensional input. The mouse’s motion typically translates into the motion of a pointer on a display, which allows for fine control of a Graphical User Interface.

The name mouse, originated at the Stanford Research Institute, derives from the resemblance of early models (which had a cord attached to the rear part of the device, suggesting the idea of a tail) to the common mouse.[1].

Operating a mechanical mouse.
1: moving the mouse turns the ball.
2: X and Y rollers grip the ball and transfer movement.
3: Optical encoding disks include light holes.
4: Infrared
LEDs shine through the disks.
5: Sensors gather light pulses to convert to X and Y velocities.

  1. KUNAL-mech 1st yr
    October 15, 2008 at 3:01 PM

    dear sir,
    Hi went through ur blog sir its amazing and awesome. Hats off to ur hard work and efforts to create it. I am blessed to be ur student and would appreciate more if u teach me this during free hours nd i will put my total interest in learning this
    yours faithfully

  2. November 12, 2008 at 1:16 AM

    Great work.

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