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Chapter Overview

Understanding Expansion Buses Configuring Expansion Cards Cables and Connectors

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Understanding Expansion Buses A system bus is the series of connections

between the CPU and the system memory. An expansion bus connects add-on devices

to the computer system. Expansion buses include the following types:

Industry Standard Architecture (ISA), Micro Channel Architecture (MCA), Extended Industry Standard Architecture (EISA)

VESA local bus (VLB), Peripheral Component Interconnect (PCI), Accelerated Graphics Port (AGP)

Institute of Electrical and Electronics Engineers (IEEE) 1394 (FireWire), universal serial bus (USB)

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Industry Standard Architecture (ISA)

Standard established by IBM Problems with ISA design

Lack of speed Compatibility problems

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Micro Channel Architecture (MCA)

Was proprietary architecture designed by IBM to defend its market position

Was able to “self configure” devices Was not backward compatible with ISA Had a 32-bit data path Has been discontinued

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Extended ISA

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VESA Local Bus (VLB)

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Peripheral Component Interconnect (PCI)

Overcomes limitations of ISA, EISA, MCA, and VLB

Has become an unofficial industry standard

Has significant differences from VLB Are also differences in PCI versions Is an evolving technology

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Accelerated Graphics Port (AGP)

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IEEE 1394 (FireWire)

Interface originally developed by Apple High-speed interface that allows up to

62 devices on a chain Advantages: hot swap, inexpensive

connectors, simple cable design Direct path to system memory Not presently a widely used standard

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Universal Serial Bus (USB)

Connects peripherals outside the computer Supports speeds of 1.5 Mbps for

asynchronous transfer and 12 Mbps for isochronous transfer

Offers the following advantages: Hot swap Recognition of new device by operating system

(OS) Ease of adding new devices

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The Most Common I/O Addresses

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Setting and Managing I/O Addresses

Non–Plug and Play I/O addresses are set with jumpers, dual inline package (DIP) switches, and software drivers.

Plug and Play devices are self-configuring and can conflict with older non–Plug and Play cards.

Devices with overlapping I/O addresses will not respond to commands.

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Interrupt Request (IRQ)

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Cascading the 8259 Chip

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Setting IRQs

Set IRQs during installation. Use hardware, software, or a

combination of both to set IRQs. Document all IRQ settings.

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Direct Memory Access

The direct memory access (DMA) chip (8237) offloads work from the CPU.

Each 8237 chip supports four devices. Two DMA chips are cascaded to provide

eight DMA channels.

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Setting and Managing DMA Channels

ECP = Extended Capabilities PortSCSI = Small Computer System Interface

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COM and Ports

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COM Ports

COM1 and COM3 share IRQ4. COM2 and COM4 share IRQ3. COM3 uses I/O port 3E8–3EF and COM1

uses 3F8–3FF. COM4 uses I/O port 2E8–2EF and COM2

uses 2F8–2FF.

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LPT Ports

You should use IRQ7 for LPT1 and IRQ5 for LPT2.

IRQ5 is typically used by sound cards. Devices other than printers can use LPT

ports. The USB is taking over many of the

parallel designs.

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Installing Expansion Cards

Read the documentation. Document addresses and DMA and IRQ

settings. Keep settings unique, and document

them.

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Parallel Printer Cables

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IEEE 1284 Printer Modes

It is important to configure the correct mode for each printer.

Each pin assignment corresponds to a specific function.

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Serial Port Cables

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Null Modem and SCSI Cables

Null modem cable: used to directly connect two computers

SCSI cable: used to connect a variety of internal and external devices

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Keyboard Cables

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Identifying Cables and Connectors

Communication Printer Monitor Game port Keyboard

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Troubleshooting Cables

Always check the cable first. Always check for loose connections. Check for bent or broken pins. Do not use force. Check for worn or frayed cables. Ensure that you are using the correct

cable. Avoid “homemade” cables.

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Summary of Connectors

DB-9, DB-25: used for serial and parallel port communications, respectively

RJ-11, RJ-12: standard telephone connectors RJ-45: network connector PS/2 (mini-DIN): supports mouse, scanners,

and some keyboards Centronics: supports printers USB: supports a variety of peripheral

devices

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Chapter Summary Expansion buses are standardized connections for

installing devices. Expansion buses have several architecture types. All devices require unique I/O addresses, IRQs, and

DMA channels. IRQ conflicts cause most problems during

installation of a new device. COM ports are used for serial devices, and LPT

ports are used for parallel devices. It is important to identify cables and connectors. Loose or poorly connected cables often cause

computer problems.