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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