Bus structures

Unit objectives Describe the primary types of buses,

and define interrupt, IRQ, I/O address, DMA, and base memory address

Describe the features and functions of the PCI bus

Describe the features and functions of the various video buses

Topic A

Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Buses

Communication pathway Defined by

– How many bits it transmits at one time– Signaling technique– Data transfer speed

Four types– Address– Data– Expansion– Video

continued

Buses, continued

Address and data buses enable: – Basic CPU operation – Interactions with memory

Expansion bus– Communication pathway for non-core

components to interact with core components

– Adapter cards add functionality– PCI bus predominant– Older buses: ISA, EISA, Micro Channel,

and PC bus

PCI bus slots

Video bus

Generates signals sent to monitor Can be built into motherboard or

adapter card Communicates over expansion or

video bus Enormous amount of data strains

expansion bus Graphic buses

– VESA or AGP– Transmit video data at high speeds

An AGP video bus slot

AGP slot

The riser bus

Brings the basic wiring and control of a function to a motherboard

Decreases cost Three riser standards:

– Advanced Communication Riser (ACR) – Audio/Modem Riser (AMR) – Communication and Networking Riser

(CNR)

Activity A-1

Examining buses

System interaction

Gain the attention of the CPU Access shared memory locations Extend the system BIOS Transfer data across the bus

Interrupts

Signal CPU that attention is needed– CPU stops what it was doing– Services the device request– Returns to its previous task

Polling– Inefficient alternative to interrupts

IRQs

Numerical addresses Help CPU identify interrupt source Enforce priority of interrupts Common IRQs

– IRQ 1: Keyboard– IRQ2: Cascade IRQs 9-15– IRQ4: COM1– IRQ6: Floppy– IRQ12: PS/2 mouse– IRQ14: Primary IDE hard drive

Device Manager: IRQs

Activity A-2

Examining IRQ assignments

I/O addresses

Identify section of shared memory Range of memory addresses Hexadecimal

Device Manager: I/O addresses

Activity A-3

Viewing your computer’s I/O address assignments

DMA channels

DMA controller relieves CPU Dedicated channels Largely replaced by other techniques,

such as bus mastering

Device Manager: DMA channels

Activity A-4

Viewing your computer’sDMA channel assignments

Base memory addresses

Devices extend system BIOS with new routines– Display adapters– SCSI controllers– IDE controllers

System BIOS locates and loads BIOS extensions using mapped memory location

Device Manager: Base memory

Activity A-5

Viewing your computer’s base memory address assignments

Topic B

Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Bus types

PCI currently most popular Historical bus types

– PC/XT– PC/AT– ISA– EISA– MCA

PC/XT bus

8-bit bus– IBM PC and IBM XT

4.77 MHz clock speed 1.6 Mbps maximum data transfer rate

(0.4 MBps) Supported IRQs 0-8 Configured with DIP switches or

jumpers

PC/XT card

PC/AT and ISA bus

16-bit bus– IBM AT, clones, 80386/486, current PCs

8 MHz clock speed 8 MBps maximum data transfer rate

ISA adapter

ISA expansion bus slot

ISA slot

PCI bus

32- or 64-bit bus– Pentium PCs

33 or 66 MHz clock speed 133-533 MBps maximum data transfer rate Up to 8 functions on a single card Up to 5 cards/slots per system Requires PnP

PCI adapter

PCIe

Newer standard Uses serial communication Link Lanes x1 (by one) x1, x2, x4, x8, x12, x16, and x32 bus

widths Can up-plug Can’t down-plug

Multifunction cards

PCI spec supports multifunction cards Up to 8 functions per card Five slots/cards per system Total of 40 expansion devices

Activity B-1

Identifying a PCI bus

Topic C

Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Need for video buses

Older PC designs just used expansion bus

Graphical interfaces involve massive amounts of graphics data

Specialized buses were developed to be fast enough

VESA local bus

32- or 64-bit bus– Pentium PCs

33 or 66 MHz clock speed Popular on 80486-based PCs Generally software configurable No longer used

VLB adapter

PCI-based video

Low-end systems: video adapter built into motherboard

Three type of video slots– PCI– PCIe– AGP

PCI is slowest of three types Share bus with all other PCI-based

devices Work well for two-monitor system

AGP standards

AGP 1.0 AGP 2.0 AGP 3.0 64-bit AGP Ultra-AGP AGP Pro Ultra-AGPII

AGP

Technically a port, not a bus Provides direct connection between video

adapter and CPU Referred to as #X Original performance benefit was accessing

and using main system memory– Direct Memory Execute (DIME)

Modern AGP cards use onboard memory, except in laptops

Multiple-monitor support Being phased out for PCIe

AGP adapter

Note the hook

AGP characteristics

32-bit bus Multiple of 33 MHz clock speed Speed “pumped” to as much as 533

MHz 266-2133 MBps maximum data

transfer rate PnP configurable

AGP slots

Typically brown; sometimes maroon or other dark color

Separated from other bus slots

High-end systems include multiple, independent AGP slots

PCIe

16x PCIe card has 4 Gbps bandwidth Dual line technology allows up to 8

GBps Simultaneous data movement

upstream and downstream Ideal for gaming and photography,

videography

A PCIe video card

Activity C-1

Identifying graphics connections

Unit summary

Described the primary types of buses, and defined interrupt, IRQ, I/O address, DMA, and base memory address

Described the features and functions of the PCI bus

Described the features and functions of the various video buses, and installed and configured an AGP adapter card