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Yonsei Yonsei University University Chapter 6 Chapter 6 External Device External Device

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Page 1: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

YonseiYonsei UniversityUniversity

Chapter 6Chapter 6

External DeviceExternal Device

Page 2: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

YonseiYonsei UniversityUniversity6-2

• External Devices• I/O Modules• Programmed I/O• Interrupt-Driven I/O• Direct Memory Access• I/O Channel and Processors• The External Interface:SCSI and FireWire

Contents Contents

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• Input / Output modules are the third critical element of the computer system (others are the CPU and the memory)

• Why one does not connect peripherals directly to the system bus– Variety of peripherals with various methods of

operation– Data transfer rate of peripherals is slow– Different data format and word lengths

• I/O module major functions– Interface to the processor and memory via the

system bus or central switch– Interface to the one or more peripheral devices by

tailored data links

OverviewOverview External DevicesExternal Devices

Page 4: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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Generic Model of an I/O ModuleGeneric Model of an I/O Module External DevicesExternal Devices

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• External device is referred to as a peripheral device

• External Device – Human readable

• VDT(video display terminal)– Machine readable

• Magnetic disk, tape systems, sensor– Communication

Peripheral devicePeripheral device External DevicesExternal Devices

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External DeviceExternal Device External DevicesExternal Devices

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Keyboard/MonitorKeyboard/Monitor

• Most common means of computer/user interaction

• Basic unit of exchange is the character• ASCII is most commonly used

External DevicesExternal Devices

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America Standard CodeAmerica Standard Code External DevicesExternal Devices

Page 9: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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ASCII Control CharactersASCII Control Characters External DevicesExternal Devices

Page 10: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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ASCII Control CharactersASCII Control Characters External DevicesExternal Devices

Page 11: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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ASCII Control CharactersASCII Control Characters External DevicesExternal Devices

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ASCII Control CharactersASCII Control Characters External DevicesExternal Devices

Page 13: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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Disk DriveDisk Drive• Disk driver exchanges data, control, status

signal with an I/O module plus the electronics for controlling the disk read/write mechanism

• Fixed-head disk– Convert the magnetic patterns on the moving disk

surface to bits in the devices buffer

• Moving-head disk– Cause disk arm to move in and out across the

disk’s surface

External DevicesExternal Devices

Page 14: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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Module FunctionModule Function• Major funtion for an I/O module

– Control and timing– Processor communication– Device communication– Data buffering– Error detection

I/O ModulesI/O Modules

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Control and timingControl and timing

• Control step of the transfer data– Processor interrogates the I/O module– I/O module returns the device status– Transfer data by means of a command to the I/O

module– I/O miodule obtains a unit of data– Data are transferred from the I/O module to the pr

ocessor

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Processor communicationProcessor communication

• Processor communication – Command decoding

• I/O module accepts commands from processor– Data

• Exchange data between processor and I/O– Status reporting

• It is important to know status of I/O module• Common status signal : BUSY, READY

– Address recognition• Each I/O device has an address• An I/O module must recognize one unique

address for each peripheral it controls

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I/O Device Data RatesI/O Device Data Rates External DevicesExternal Devices

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Device communicationDevice communication

• Device communication involves commands, ststus information, and data

External DevicesExternal Devices

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Data bufferingData buffering

• Data coming from main memory are sent to an I/O module in a rapid burst

• Data are buffered in the I/O module and then sent to the peripheral device at it data rate

• In opposite direction, data I/O module must be able to operate at both device and memory speeds.

External DevicesExternal Devices

Page 20: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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Error detectionError detection

• I/O module is responsible for error detection and for subsequently reporting errors to the processor

External DevicesExternal Devices

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I/O Module StructureI/O Module Structure• Connect to the rest of the computer through a set of

signal lines• I/O module function to allow the processor to view a

wide range of devices in a simple-minded way• I/O channel

– Quite primitive and requires detailed control– Commonly seen on the microcomputer

• I/O controller – Used on mainframes

External DevicesExternal Devices

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Block Diagram of an I/O ModuleBlock Diagram of an I/O Module External DevicesExternal Devices

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Three Techniques for I/O OperationsThree Techniques for I/O Operations

• Programmed I/O • Interrupt driven I/O• DMA

Programmed I/OProgrammed I/O

No Interrupts Use of Interrupts

I/O-to-memory transfer through processor

Programmed I/O Interrupt-driven I/O

Direct I/O-to-memory transfer

Direct memory access

(DMA)

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OverviewOverview

• Processor execute program that give it direct control I/O operation

• I/O module perform the requested action• Set the appropriate bits in the I/O status regist

er• I/O module takes no further action to alter the

processor• It does not interrupt the processor

Programmed I/OProgrammed I/O

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I/O CommandsI/O Commands• Four type I/O commands

– Control • Activate a peripheral and tell it what to do

– Ex. Megnetic-tape rewind, forward…– Test

• Test a various ststus conditions associated with an I/O module and its peripherals

– Read• Obtain an item of data from the peripheral and p

lace it in an internal buffer(Fig6.4 data register)– Write

• Take an item of data(byte or word) from the data bus and transmit that data item to the peripherals

Programmed I/OProgrammed I/O

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Tree Techniques for Input of a Block of DataTree Techniques for Input of a Block of DataProgrammed I/OProgrammed I/O

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I/O InstructionsI/O Instructions• Instruction are easily mapped into I/O

commands• Form of the instruction depends on the way

external devices are• I/O devices is given a unique identifier or

address

Programmed I/OProgrammed I/O

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I/O InstructionsI/O Instructions• Two modes of addressing

– Memory mapped I/O• Single address space for memory locations and

I/O devices• Same machine instruction to access both

memory and I/O devices– Isolated I/O

• Address space for I/O is isolated from memory

• Need I/O or memory select lines• Special commands for I/O

Programmed I/OProgrammed I/O

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Memory-Mapped and Isolated I/OMemory-Mapped and Isolated I/O Programmed I/OProgrammed I/O

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Interrupt-Driven I/OInterrupt-Driven I/O

• Problem of programmed I/O– Processor wait a long time for the I/O module of

concern to be ready for either reception or transmission of data

• Alternative– Processor issue an I/O command to a module and

go on to do some other useful work– Interrupt the processor to request service when it

is ready to exchange data with the processor– Execute data transfer and resume its former

processing

Interrupt-Driven I/OInterrupt-Driven I/O

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Interrupt-Driven I/OInterrupt-Driven I/O

• Interrupt I/O is more efficient than programmed I/O because it eliminate needless waiting

• Interrupt I/O still have much processor time

Interrupt-Driven I/OInterrupt-Driven I/O

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Simple Interrupt ProcessingSimple Interrupt Processing Interrupt-Driven I/OInterrupt-Driven I/O

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Interrupt ProcessingInterrupt Processing

• Sequence of hardware events1. Device issues an interrupt signal to processor

2. Processor finish execution of execution of current instruction

3. Processor signals acknowledgment of interrupt

4. Processor push PSW and PC onto control stack

5. Processor loads new PC value based on interrupt

6. Save remainder of process state information

7. Process interrupt restore process state information

8. Restore process state information

9. Restore old PSW and PC

Interrupt-Driven I/OInterrupt-Driven I/O

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Design IssuesDesign Issues• How does the processor determine which dev

ice issued the interrupt• If multiple interrupts have occurred, how does

the processor decide which one to process?• Four device identification

– Multiple interrupt lines– Software poll– Daysy chain(hardware poll, vectored)– Bus arbitration(vectored)

Interrupt-Driven I/OInterrupt-Driven I/O

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Changes in Memory & RegisterChanges in Memory & Register Interrupt-Driven I/OInterrupt-Driven I/O

(a) Interrupt occurs after instruction at location N(a) Interrupt occurs after instruction at location N

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Changes in Memory & RegisterChanges in Memory & Register Interrupt-Driven I/OInterrupt-Driven I/O

(b) Return from interrupt(b) Return from interrupt

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Multiple Interrupt linesMultiple Interrupt lines• Most straightforward approach to the problem• Impractical to dedicate bus lines or processor

pins to interrupt lines

Interrupt-Driven I/OInterrupt-Driven I/O

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Software PollSoftware Poll

• On interrupt, processor branchs to an interrupt-service routine which it is to poll each I/O module to determine which module caused the interrupt

• Poll is in the form of a separate command line(TESTI/O)

• Each l/O module contain an addressable status register

• Read status register of each IO module to identify the interrupting module

• Disadvantage is time consuming

Interrupt-Driven I/OInterrupt-Driven I/O

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Daisy ChainDaisy Chain

• Hardware poll• Vectored interrupt

– Vector • A word on the data lines• Address of the I/O module or unique identifier

– Processor use vector as a pointer to the appropriate device routine

– Avoid the need to execute a general interrupt-service routine first

Interrupt-Driven I/OInterrupt-Driven I/O

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Bus ArbitrationBus Arbitration

• I/O module must first gain control of the bus• One module can raise the line at a time• On interrupt, it respond on the interrupt ack li

ne• Requesting module place its vector on the dat

a lines

Interrupt-Driven I/OInterrupt-Driven I/O

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Intel 82C59A Interrupt ControllerIntel 82C59A Interrupt Controller

• Intel 80396 provide a single interrupt request(INTR) and single ack(INTA)

• External interrupt arbiter, 82C59A• 82C59A manage interrupt• Interrupt mode

– Fully nested• Interrupt request are ordered in priority from 0(I

R0) through 7(IR7)– Rotating

• Lowest priority in the group– Special mask

• Processor inhibit interrupt from certain devices

Interrupt-Driven I/OInterrupt-Driven I/O

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82C59A Interrupt Controller82C59A Interrupt Controller Interrupt-Driven I/OInterrupt-Driven I/O

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Intel 82C55A Intel 82C55A

• General-purpose I/O module designed for use with the Intel 80386 processor

• Next page Fig 6.10

Interrupt-Driven I/OInterrupt-Driven I/O

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Intel 82C55A Intel 82C55A Interrupt-Driven I/OInterrupt-Driven I/O

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Keyboard/Display InterfaceKeyboard/Display Interface Interrupt-Driven I/OInterrupt-Driven I/O

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Drawbacks of I/ODrawbacks of I/O

• Processor intervene in data transfer between memory and an I/O module

• Inherent drawback – I/O transfer rate is limited– Processor is tied up in managing an I/O transfer

• More efficient technique is required:– Direct memory access(DMA)

Direct memory accessDirect memory access

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DMA Block DiagramDMA Block Diagram Direct memory accessDirect memory access

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DMA FunctionDMA Function

• DMA involves an additional module on system bus

• DMA module take over control of the system from processor

• Cycle stealing – DMA module in effect steals a bus cycle

Direct memory accessDirect memory access

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DMA FunctionDMA Function• Issue a command to the DMA module, by

sending to the DMA module the following information– Whether a read or write is requested, using the

read or write control line between the processor and the DMA module

– Address of I/O device involved, communicated on the data lines

– Starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register

– The number of words to be read or written, again communicated via the data lines and stored in the data count register

Direct memory accessDirect memory access

Page 50: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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DMA FunctionDMA Function

• DMA module transfer the entire block of data,– One word at a time – Directly to or from memory– Without going through the processor

• When transfer complete, DMA module sends an interrupts signal to processor

• Processor is involved only at the beginning and end of the transfer

Direct memory accessDirect memory access

Page 51: Yonsei University Chapter 6 External Device. Yonsei University 6-2 External Devices I/O Modules Programmed I/O Interrupt-Driven I/O Direct Memory Access

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DMA & Interrupt Break pointDMA & Interrupt Break point Direct memory accessDirect memory access

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Alternative DMA ConfigurationAlternative DMA Configuration Direct memory accessDirect memory access

• Single-Bus, Detached DMA

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Alternative DMA ConfigurationAlternative DMA Configuration Direct memory accessDirect memory access

• Single-Bus, Integrated DMA-I/O

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Alternative DMA ConfigurationAlternative DMA Configuration Direct memory accessDirect memory access

• I/O Bus

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The evolution of the I/O FunctionsThe evolution of the I/O Functions

• Evolutionary step1. CPU directly controls a peripheral device

2. Controller or I/O module is added

3. Same configurations is used, but now interrupts are employed

4. I/O module is given direct access to memory via DMA

5. I/O module is enhanced to become a processor in its own right, with a specialized instruction set tailored for I/O (I/O channel)

6. I/O module has a local memory of its own and is a computer in its own right (I/O processor)

I/O Channels & ProcessorsI/O Channels & Processors

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The evolution of the I/O FunctionsThe evolution of the I/O Functions

• More and more of the I/O function is performed without CPU involvement

I/O Channels & ProcessorsI/O Channels & Processors

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Characteristics of I/O ChannelsCharacteristics of I/O Channels• I/O channel an extension of DMA concept• I/O channel has the ability to execute I/O instr

uction• CPU does not execute I/O instruction• Two type of I/O channel

– Selector channel• Control multiple high-speed devices• Transfer of data with one of those devices

– Multiplexor channel• Handle I/O with multiple devices at the same ti

me

I/O Channels & ProcessorsI/O Channels & Processors

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I/O Channel ArchitectureI/O Channel Architecture I/O Channels & ProcessorsI/O Channels & Processors

(a)Selector

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I/O Channel ArchitectureI/O Channel Architecture I/O Channels & ProcessorsI/O Channels & Processors

(b)Multiplexor

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Type of InterfaceType of Interface

• Parallel interface– Multiple line connecting the I/O module and the

peripheral– Multiple bits transferred simultaneously– Used for higher speed peripherals(tape,disk)

• Serial interface– One line used to transmit data – Bits must be transmitted one at a time– Printer, terminals

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Dialogue for a Write OperationDialogue for a Write Operation

1. I/O module send a control signal

2. Peripheral acknowledges the request

3. I/O module transfer data

4. Peripheral acknowledges receipt of the data

(read operation proceeds similary)

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Parallel and Serial I/OParallel and Serial I/O

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Point-to-Point & MultipointPoint-to-Point & Multipoint

• Point-to-point– Dedicated line between I/O module and external

device– On small system(PC), include keyboard, printer,

external modem

• Multipoint– Used to support external mass storage

devices(disk, type) and multimedia devices(CD-ROM,video)

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Small Computer InterfaceSmall Computer Interface

• SCSI– Popularized in the Macintosh in 1984– Now widely used on Mac, Windows/Intel system,

workstation

• SCSI Version– SCSI-1 :

• 8 data lines and operate at a clock speed of 5MHz of a data rate of 5 Mbytes/s

– SCSI-2 :• Optional expansion of the data lines to 16-32

and increase of the clock speed to 10 MHz• Maximum data rate of 20 or 40 Mbytes/s

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Signals and PhasesSignals and Phases• Bus Free

– No device is using the bus

• Arbitration– Enable one device to gain control of the bus

• Selection– Enable an initiator to select a target to perform a fu

ncion

• Reselection– Enable a target to reconnect to an initiator to resu

me an operation

• Command– Enable target to request the command information

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Signals and PhasesSignals and Phases

• Data– Enable the target to request the transfer of data

• Status– Enable the target to request that status information

be sent from the target to the initiator

• Message– Enable the target to request the transfer of one or

more messages

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Bus PhasesSCSI Bus Phases External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Control LinesSCSI Control Lines• BSY

– Set to indicate the bus is busy

• SEL – Select a target to perform a command

• C/D– Indicate whether data on the data bus is Control or

Data information

• I/O– Control the direction of data movement

• MSG– Indicate to the initiator that the information being tr

asferred is a message

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Control LinesSCSI Control Lines• REQ

– Request a data information transfer

• ACK– Acknowkedge a REQ from traget

• ATN– Inform the target that it has a message available fo

r transfer

• RST– Used to reset the bus

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Bus SignalsSCSI Bus Signals

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Timing DiagramSCSI Timing Diagram External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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MessagesMessages• Command complete• Disconnect• Initiator Detected Error• Abort

– Sent from initiator to the target to clear the present operation

• Synchronous Data Transfer– Exchanged between initiator and target to

establish synchronous data transfer

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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CommandsCommands

• Steps for execution of command– Target acquires and decides command information– Data is transferred to or from the target– Target generates and returns status information

• Fields of CDB– Operation code– Logical unit number– Logical block address– Transfer length– Parameter list length– Allocation length– Control

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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SCSI Command Block FormatSCSI Command Block FormatExternal Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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CommandsCommands

• Mandatory – Inquiry– Request Sense– Send Diagnostic– Test unit ready

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Fire Wire Serial BusFire Wire Serial Bus

• FireWire– IEEE standard 1394, for a high-performance serial

bus

• Advantages– High speed– Low cost– Easy to implement

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Fire Wire Serial BusFire Wire Serial Bus

• Use serial transmission (bit at a time) rather than parallel

• Computers are getting physically smaller • Provide a single I/O interface with a simple

connector • User can reach behind the machine and plug

it in without looking

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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FireWire ConfigurationsFireWire Configurations

• Use a daisy chain• Provide for what is known as hot plugging• With SCSI, both ends of the bus must have

terminators and each device must be assigned a unique address as part of the configuration

• No terminators

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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FireWire ConfigurationsFireWire Configurations

• System automatically perform a configuration function to assign addresses

• Tree structured configuration is possible• Three layer of the stack

– Physical layer– Link layer– Transaction layer

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Comparison of SCSI&FireWireComparison of SCSI&FireWire External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Physical layerPhysical layer

• Several alternative transmission media and their connectors

• Tree structured arrangement of the node

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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FireWire Protocol StackFireWire Protocol Stack External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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Link LayerLink Layer

• Tow type of transmission– Asynchronous– Isochronous

• Subaction’s five time period– Arbitration sequence– Packet transmission– Acknowledgement gap– Acknowledgment– Subaction gap

External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire

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FireWire SubactionsFireWire Subactions External Interface: SCSExternal Interface: SCSI and FireWireI and FireWire