Bus System-Chapter 4

8/14/2019 Bus System-Chapter 4

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BUS SYSTEM

CHAPTER 4


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OVERVIEW

1. Explain CPU oriented bus to

architecture oriented bus systems.

2. Explain bus structure and operation.

Electronic bus interface.

Electrical bus interface.Bus operation.

Block transfer and Direct Memory Access

(DMA).

Interrupt operation.


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3. VMEbus (IEEE 1014)

Data transfer.

Interrupt priority.

4. Multibus II (ANSI/IEEE 1296)Data transfer.

operation.


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5. Other bus

standards.

EISA

NuBus (IEEE 1196)

Multibus I (IEEE

796)STD (IEEE 961)


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What is a BUS ?

A bus can be thought as a highway for digital signal

It consists of a set physical connection (printed circuit

traces or wires)

Electrically, a bus is a group of specified voltage levels and

current levels and signal that allow the various devices

connected to the bus to work properly together.

it consists of a standard set of specification

Physically, bus is a set of conductive paths that serves to

interconnect two or more components of a system


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BUS SYSTEM in MICROCOMPUTER SYSTEM

InternalBus External or

I/O BusInterconnect the various

components within acomputer system.

The processor, memory,disc drive and interface

cards

Signal transmission betweencomputer and the outside

world

Video, monitor, keyboard,

mouse and printer


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A bus is multiplexed so that any of thedevices connected to it can either send or

receive data to or from one of the other

devices

A sending device is called a SOURCE

A receiving device is called ACCEPTOR

At any given time, there is only one sourceactive.


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The process of establishing communication

between acceptor and Source is called

HANDSHAKING

Source

e.g RAM

Acceptor

e.g CPU

Prepare to receiveData ready

Ready to receiveData accepted

Control bus


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How to interface the source to a bus system?

Tristate drivers (buffers)

are normally used

Input Output

Enable


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Input Output

Enable

Active-HIGH enable

Input Output

Enable

Active-LOW enable


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Tristate Buffer OperationSwitching action

HIGH HIGH

HIGH

Active-HIGH enable

LOW LOW

LOW

orHIGH

disconnected

LOW


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HIGH HIGH

LOW

Active-LOW enable

LOW LOW

LOWor

HIGH

disconnected

HIGH


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Source A

e.g RAM

Source B

e.g ROM

Data BusSelectTristate buffer

Tristate

Buffer

is used to

connect ordisconnect

a source

to a bus

10

1

0

1

0

0

0

1

0

1 0 1 0

0 0 1 0


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In general the block diagram is shown below

CPU

SourceA SourceB

Data Bus

Tristate buffer

Active-HIGH

Tristate buffer

Active-LOWSelect

1100

Register


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Multiplexed I/OsSome devices has a port for input and

output lines to send and receive data

Use BIDIRECTIONAL TRISTATE DRIVERS


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SENDING DATAURCE

I/O

Bus line

0

1

(low)

1


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RECEIVING DATAURCE

I/O

Bus line

1

1

(high)

1


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Source A

e.g RAM

Data BusSelect

Tristate buffer

10

0

0

1

0 0 1

1

1

1

SENDDATA

RECEIVDATA


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STANDARD BUSES

INTERNAL

BUSES

EXTERNAL

BUSES

LOCAL BUSPCIISARS-232CIEE3 1394USB

IEEE 488SCSI

SERIAL I/OINTERFACE

BUSES

PARALLEL I/OINTERFACE

BUSES


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INTERNAL BUSES

Internal buses in a computer carry addresses,

data and control signals between the CPU,

memory, disc drives, expansion slot and

other internal devices


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Personal computer consists

of 3 types of internal buses

1. Local bus

2. PCI (peripheral Control Interconnect)

Bus

3. ISA (Industry Standard Architecture)

Bus


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LOCAL BUS

Primary busThis bus connects directly to the

microprocessor (CPU).

It consists of the data bus, the address bus

and the control bus


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PCi

Secondary busThis bus is used to interface the

microprocessor with external devices via

expansion slot (connectors)First introduced by Intel in 1993Has become the standard PC interface busPCI is a 64-bit bus

PCI can connect the CPU to hard drive viaexpansion slots with adapter cardPCI support plug-and-play

PCI BUS


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Was developed by IBMMost modern PC use this bus

It has 8-bit or 16-bit data bus

An expanded version EISA (Extended

industry Standard Architecture) that provide32-bit data bus

ISA BUS


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EXTERNAL BUSES

External bus is used to interface the

computer to the outside world and the

peripheral equipment e.g a video monitor,

keyboard, mouse etc.External devices are connected to a

computer via an input/output interface

called a PORT

2 T f C t P t


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2 Types of Computer Ports

PARALLELPORTS

SERIALPORTS

Is used for serial datacommunication

Is used for paralleldata communication

Only 1 bit is

transferred at atime

Modem

At least 1 byte is

transferred at atime

Test & measurementequipment

Hard disc rinter


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SERIAL I/O PORTS


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2. IEEE 1394

Used for interfacing withgraphics and video

peripherals such as digitalcamera.

Often called FIREWIRESupport hot plugging

SERIAL I/O PORTS

SERIAL I/O PORTS


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Eventually replace most other existinglow-to-medium-speed serial and parallel

bus standard

Permits both plug-and-play and hotplugging

Support 2 data transfer rate high speed rate 12Mbps

low-speed rate 1.5Mbps

3.USB (Universal serial bus)

SERIAL I/O PORTS


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PARALLEL I/O PORTS


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2. SCSI (Small Computer

System Interface)

Widely used as a standard for interfacingPC and peripherals like Hard disk, Printer

and CD-ROM.Types of SCSISCSI-2, Wide SCSI, Fast SCSI, Fast wide

SCSI, Ultra SCSI, SCSI-3, Ultra SCSI-2, WideUltra SCSI-2

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Bus System-Chapter 4