Chapter Overview Understanding Expansion Buses Configuring Expansion Cards Cables and Connectors

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)

Industry Standard Architecture (ISA) Standard established by IBM Problems with ISA design Lack of speed Compatibility problems

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

Extended ISA

VESA Local Bus (VLB)

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

Accelerated Graphics Port (AGP)

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

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

The Most Common I/O Addresses

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.

Interrupt Request (IRQ)

Cascading the 8259 Chip

Setting IRQs Set IRQs during installation. Use hardware, software, or a combination of both to set IRQs. Document all IRQ settings.

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.

Setting and Managing DMA Channels ECP = Extended Capabilities Port SCSI = Small Computer System Interface

COM and Ports

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.

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.

Installing Expansion Cards Read the documentation. Document addresses and DMA and IRQ settings. Keep settings unique, and document them.

Parallel Printer Cables

IEEE 1284 Printer Modes It is important to configure the correct mode for each printer. Each pin assignment corresponds to a specific function.

Serial Port Cables

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

Keyboard Cables

Identifying Cables and Connectors Communication Printer Monitor Game port Keyboard

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.

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

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.