CA Lec#Buses

7/28/2019 CA Lec#Buses

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Buses

Characteristics,

Types &Uses.


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Buses Common Characteristics

Multiple devices communicating over a single set ofwires

Only one device can talk at a time or the message is

confused Each line or wire of a bus can at any one time contain a

single binary digit. Over time, however, a sequence ofbinary digits may be transferred

These lines may and often do send information in parallel A computer system may contain a number of different

buses


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Buses Structure

Serial versus parallel

Around 50-100 lines although it's possible tohave as few as 3 or 4

Lines can be classified into one of four groups

Data lines

Address Lines

Control Lines Power


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Physical Implementations

Parallel lines on circuit boards

(ISA or PCI)

Ribbon cables (IDE)


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Physical Implementations (continued)

Strip connectors on mother

boards (PC104)

External cabling (USB or

Firewire)


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Buses

Definition: a collection of wires with a

common purpose

Each wire is called a line

Typically, buses carry information from one

place to another


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Ports

CPU

RAM

Disk

controller

Graphics

card

Sound

card

Networkcard

Printer

Mouse

Keyboard

ModemMonitor

Speakers

bus

Computer


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Types of Buses

Point-to-point

Serial

port

Modem

Control

unit ALU


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Types of Buses

Multipoint

Computer

CPU

Disk controller

Computer

Computer Computer

Memory

Video controller


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Point-to-point vs. Multipoint

Point-to-point and multipoint refer to signaling propagation

Point-to-pointSignal from a source is reachable by onlyone node.

MultipointMany nodes can sense the same signal from a

source. Point-to-point requires a dedicated connection directly linked

between two nodes

Host should have one connector for each devices

Multipoint can share single connection from host Devices may attach directly to a share bus or through

HUBs


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Point-to-point vs. Multipoint

Point-to-point

Each connection musthave a dedicated circuit

Speed on a connectioncan differ from theothers

Defected devices cannotinterfere others

More expensive if wewant to connect to manydevices

Multipoint

Devices usually sharesame connection fromhost

All devices shouldsynchronize to eachother

A defected device can

make the whole systemmalfunction

Cheaper to increase thenumber of deviceconnected to a system


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Buses Inside a Computer

Data bus

Address bus

Control bus

Memory

I/OModule

I/O Device

CPUMotherboard Many

configurations

possible


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Data Bus

Carries data between the CPU and memory or I/O

devices

Bi-directional

Data transferred out of the CPU for write operations

Data transferred into the CPU for read operations

Typical sizes: 8, 16, 32, 64 lines

Signal names: D0, D1, D2, D3, etc.


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Address Bus

Carries an address from the CPU to Memory or I/O

devices

Unidirectional

The address is always supplied by the CPU(There is one exception to this, which well discuss later.)

Typical sizes: 16, 20, 24 lines

Signal names:

A0, A1, A2, A3, etc.


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Control Bus

Collection of signals for coordinating CPU activities

Each signal has a unique purpose

Typical sizes: 10-20 lines

Signals are output, input, or bi-directional Typical signals

/RD (read)

/WR (write)

CLK (clock)

/IRQ (interrupt request)

etc.

CA Lec#Buses

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