Input - output organzation

Shree s’ad vidyamandal institute of
technology
DEPARTMENT OF ENGINEERING
INFORMATION TECHNONLGY

• Daxesh Chauhan 130450116004
• Patanvadiya Nidhi 130450116020
• Thakor Rahual 130450116042
• Yadav Deepak 130450116045

Input Output Organization
IO Interface
Modes of transfer
Interrupt
Direct Memory Access
Introduction to IO Processor

IO Interface
• IO interface provides a method for
transferring information between internal
storage and external I/O devices.
• I/O devices can not directly communicate with
the CPU due to various differences between
them.
• The major differences are:

• I/O bus is attached to all peripherals.
• Interface monitors the address on address bus.
• If it find its own address, it activates path
between bus line and device.
• All the other devices are disabled by their
interfaces.
• Data to read or write is made available in the data
bus.
• IO command is made available in the control bus.

• There are four types of IO command:
– Control Command
– Status Command
– Output Data Command
– Input Data Command

IO versus Memory bus
• Like IO bus Memory bus also contain data,
address and control lines.
• There are 3 ways in which computer bus
communicates with memory and IO.

• In the first method, CPU has independent set
of buses for both memory and IO. It is done in
computers that has separate IOP and CPU.
• In second method computers use common
bus to transfer data between IO or memory
and CPU. And separate read and write lines.
• IO read/write is enabled during IO transfer
and memory read/write is enabled during
memory transfer.

• This configuration isolates all I/O interface
address with the memory address and is
referred to as Isolated IO method.
• In third method same address space is used
for both memory and IO interface. They have
only one set of read and write signals.
• Computer treats interface as being part of the
memory system.

• It assign address for each interface which
cannot be used for memory words.
• This configuration is referred to as memory-
mapped IO.

Modes of transfer
• Data transfer between computer and IO
device can be handle in the following ways:
– Programmed IO
– Interrupt-Initiated IO
– Direct Memory Access(DMA)

Programmed IO
• Each data transfer is initiated by an instruction
in the program.
• CPU stays in the program loop until IO unit
indicates it is ready for the data transfer.
• It is time consuming process since it keeps
processor busy needlessly.

• The transfer of data requires three
instructions:

Interrupt Initiated IO
• In this type of IO, computer does not check
the flag. It continue to perform its task.
• Whenever any device wants the attention, it
sends the interrupt signal to the CPU.
• CPU then deviates from what it was doing,
store the return address from PC and branch
to the address of the subroutine.

• There are two ways of choosing the branch
address:
– Vectored Interrupt
– Non-vectored Interrupt
• In vectored interrupt the source that interrupt
the CPU provides the branch information. This
information is called interrupt vectored.
• In non-vectored interrupt, the branch address is
assigned to the fixed address in the memory.

Priority Interrupt
• There are number of IO devices attached to the
computer.
• They are all capable of generating the interrupt.
• When the interrupt is generated from more than
one device, priority interrupt system is used to
determine which device is to be serviced first.
• Devices with high speed transfer are given higher
priority and slow devices are given lower priority.

• Establishing the priority can be done in two
ways:
– Using Software
– Using Hardware
• A pooling procedure is used to identify highest
priority in software means.

Polling Procedure
• There is one common branch address for all
interrupts.
• Branch address contain the code that polls the
interrupt sources in sequence. The highest
priority is tested first.
• The particular service routine of the highest
priority device is served.
• The disadvantage is that time required to poll
them can exceed the time to serve them in large
number of IO devices.

Using Hardware
• Hardware priority system function as an overall
manager.
• It accepts interrupt request and determine the
priorities.
• To speed up the operation each interrupting
devices has its own interrupt vector.
• No polling is required, all decision are established
by hardware priority interrupt unit.
• It can be established by serial or parallel
connection of interrupt lines.

Serial or Daisy Chaining Priority.
• Device with highest priority is placed first.
• Device that wants the attention send the
interrupt request to the CPU.
• CPU then sends the INTACK signal which is
applied to PI(priority in) of the first device.
• If it had requested the attention, it place its
VAD(vector address) on the bus. And it block
the signal by placing 0 in PO(priority out)

• If not it pass the signal to next device through
PO(priority out) by placing 1.
• This process is continued until appropriate
device is found.
• The device whose PI is 1 and PO is 0 is the
device that send the interrupt request.

Parallel Priority Interrupt
• It consist of interrupt register whose bits are
set separately by the interrupting devices.
• Priority is established according to the
position of the bits in the register.
• Mask register is used to provide facility for the
higher priority devices to interrupt when
lower priority device is being serviced or
disable all lower priority devices when higher
is being serviced.

• Corresponding interrupt bit and mask bit are
ANDed and applied to priority encoder.
• Priority encoder generates two bits of vector
address.
• Another output from it sets IST(interrupt
status flip flop).

Direct Memory Access(DMA)
• In DMA there is direct communication
between memory and the peripheral devices.
• CPU is idle and has no control over the
memory buses.
• DMA controller uses buses and transfer the
data directly between I/O devices and
memory.

• BR(Bus Request) signal is used by DMA
controller to request CPU for the buses.
• CPU then places the bus on the high
impedance state which behave like open
circuit.
• CPU then activates BG(Bus Grant) signal to
acknowledge BR signal.
• DMA now has full control over the buses and
perform the transfer.

• Transfer can be perform in two ways:
– Burst Transfer
– Cycle Stealing
• In burst transfer, a number of memory word is
transfer in a continuous burst. It is done while
communicating with fast devices and can’t be
stopped or slow down.
• In cycle stealing, one data word is transfer at a
time.
• CPU delays it operation for one cycle during
which DMA transfer takes place.

DMA Controller
• It communicates with CPU through data bus and
control lines.
• Registers in DMA are selected by CPU by enabling
DS and RS.
• RD and WR signals are for read and write
operation.
• When BG=0 CPU can communicate with DMA
register for read or write operation.
• When BG=1 DMA communicate directly with the
memory.

DMA Controller
• It has three register: address, word count and
control register.
• Address register contain address which specify
the location of memory to read or write.
• It is incremented after each word is transferred
into memory.
• Word count register holds the number of words
to be transferred.
• It is decremented by one after each word is
transferred into memory and regularly check for
zero.

• Control Register specify the mode of transfer.
• DMA is first initialized by CPU. After that DMA
continue to transfer data.
• CPU initialize the DMA by sending the following
information through the data bus:
– Starting address of memory block for read or write.
– The word count or number of words to read or write.
– Control to specify mode such as read or write.
– Control to start DMA

• Once DMA is initialized, CPU stop
communicating with DMA unless it receive
interrupt signal or if it wants to check how
many words has been transferred.

Input-Output Processor(IOP)
• It is a processor with direct memory access
capability that communicates with IO devices.
• IOP is similar to CPU except that it is designed
to handle the details of IO operation.
• Unlike DMA which is initialized by CPU, IOP
can fetch and execute its own instructions.
• IOP instruction are specially designed to
handle IO operation.

IOP
• Memory occupies the central position and can
communicate with each processor by DMA.
• CPU is responsible for processing data.
• IOP provides the path for transfer of data
between various peripheral devices and memory.
• Data formats of peripherals differ from CPU and
memory. IOP maintain such problems.
• Data are transfer from IOP to memory by stealing
one memory cycle.

IOP
• Instructions that are read from memory by
IOP are called commands to distinguish them
from instructions that are read by the CPU.

Input - output organzation

Recommended

More Related Content

What's hot (20)

Viewers also liked (16)

Similar to Input - output organzation (20)

More from daxesh chauhan (7)

Recently uploaded (20)

Input - output organzation