UNIT 5 INPUT OUTPUT.pptx computer

03/15/2025 1
Ms. Deepshikha Rai
Department of MCA
Computer Organization and Architecture (BMC
105)
Unit - 5
INPUT/OUTPUT
Ms. Deepshikha Rai Asst. Prof. IMS Engineering College

03/15/2025
Ms. Deepshikha Rai Asst. Prof. IMS Engineering College 2
Introduction to Input-Output Interface
 Input-Output Interface: The method that is used to transfer information between internal storage
and external I/O devices is known as I/O interface
 A peripheral device is that which provide input and output for the computer, it is also called Input-
Output devices. For Example: A keyboard and mouse provide Input to the computer are called input
devices while a monitor and printer that provide output to the computer are called output
devices.
 Just like the external hard-drives, there is also availability of some peripheral devices which are
able to provide both input and output.

03/15/2025
Input-Output Interface
 The nature of peripheral devices is
electromagnetic and electro-mechanical.
The nature of the CPU is electronic. There
is a lot of difference in the mode of
operation of both peripheral devices and
CPU.
 There is a special need of the additional
hardware to resolve the differences
between CPU and peripheral devices to
supervise and synchronize all input and
output devices.

03/15/2025
Functions of Input-Output
Interface:
1. It is used to synchronize the operating speed of CPU with
respect to input-output devices.
2. It selects the input-output device which is appropriate for the
interpretation of the input-output device.
3. It is capable of providing signals like control and timing signals.
4. In this data buffering can be possible through data bus.
5. There are various error detectors.
6. It converts serial data into parallel data and vice-versa.
7. It also convert digital data into analog signal and vice-versa.

03/15/2025
Input Output Ports
 Ports: The connection point acts as an interface between the computer and external devices
like printers, modems, etc
 There are two types of ports :
 Internal Port: It connects the system’s motherboard to internal devices like hard disk, CD drive,
internal Bluetooth, etc.
 External Port: It connects the system’s motherboard to external devices like a mouse, printer,
USB, etc.

03/15/2025
Types of Computer Ports
 There are different types
of ports available:
1. Serial port
2. Parallel port
3. USB port
4. PS/2 port
5. VGA port
6. Modem port
Sockets
Infrared Port
Game Port
Digital Video Interface(DVI) Port
Ethernet Port
7.FireWire Port
8. Sockets
9. Infrared Port
10. Game Port
11. Digital Video Interface(DVI) Port
12. Ethernet Port

03/15/2025
Input Output Ports

03/15/2025
Interrupts
 An interrupt is a signal emitted by hardware or software when a process or an
event needs immediate attention.
 It alerts the processor to a high-priority process requiring interruption of
the current working process.
 In I/O devices, one of the bus control lines is dedicated for this purpose and is
called the Interrupt Service Routine (ISR).
 When a device raises an interrupt at the process, the processor first
completes the execution of an instruction. Then it loads the Program
Counter (PC) with the address of the first instruction of the ISR. Before
loading the program counter with the address, the address of the
interrupted instruction is moved to a temporary location. Therefore, after
handling the interrupt, the processor can continue with the process.

03/15/2025
Interrupts
 While the processor is handling the interrupts,
it must inform the device that its request has
been recognized to stop sending the interrupt
request signal. Also, saving the registers so that
the interrupted process can be restored in the
future increases the delay between the time an
interrupt is received and the start of the
execution of the ISR. This is called Interrupt
Latency.

03/15/2025
 A single computer can perform only one computer instruction at a time. But,
because it can be interrupted, it can manage how programs or sets of
instructions will be performed.
 This is known as multitasking. It allows the user to do many different things
simultaneously, and the computer turns to manage the programs that the user
starts. Of course, the computer operates at speeds that make it seem like all
user tasks are being performed simultaneously.

03/15/2025
Types of Interrupt
 Interrupt signals may be issued in response to hardware or software events.
These are classified as hardware interrupts or software interrupts,
respectively.

03/15/2025
1. Hardware Interrupts
 A hardware interrupt is a condition related to the state of the hardware that may be signaled by an
external hardware device, e.g., an interrupt request (IRQ) line on a PC, or detected by devices
embedded in processor logic to communicate that the device needs attention from the operating
system. For example, pressing a keyboard key or moving a mouse triggers hardware interrupts that
cause the processor to read the keystroke or mouse position.

03/15/2025
2. Software Interrupts
 The processor requests a software interrupt upon executing particular instructions or when
certain conditions are met. Every software interrupt signal is associated with a particular
interrupt handler.
 A software interrupt may be intentionally caused by executing a special instruction that invokes
an interrupt when executed by design. Such instructions function similarly to subroutine calls
and are used for various purposes, such as requesting operating system services and interacting
with device drivers.

03/15/2025
Handling Multiple Devices

03/15/2025
 1. Polling
 Polling is a method of controlling the access to a transmission medium
which is shared by a number of stations.
In polling, the first device encountered with the IRQ bit set is to be serviced
first, and appropriate ISR is called to service the same. It is easy to
implement, but a lot of time is wasted by interrogating the IRQ bit of all
devices.
 2. Vectored Interrupts
In vectored interrupts, a device requesting an interrupt identifies itself
directly by sending a special code to the processor over the bus. This enables
the processor to identify the device that generated the interrupt. The special
code can be the starting address of the ISR or where the ISR is located in
memory and is called the interrupt vector.

03/15/2025
 3. Interrupt Nesting
In this method, the I/O device is organized in a priority structure. Therefore,
an interrupt request from a higher priority device is recognized, whereas a
lower priority device is not. The processor accepts interrupts only from
devices/processes having priority more than it.
Processors priority is encoded in a few bits of PS (Process Status register), and
it can be changed by program instructions that write into the PS. The
processor is in supervised mode only while executing OS routines, and it
switches to user mode before executing application programs.

03/15/2025
Mode of data Transfer:
 The binary information that is received from an external device is usually
stored in the memory unit.
 The information that is transferred from the CPU to the external device is
originated from the memory unit.
 CPU merely processes the information but the source and target is always the
memory unit.
 Data transfer between CPU and the I/O devices may be done in different
modes.

03/15/2025
 Data transfer to and from the peripherals may be done in any of the three
possible ways
1. Programmed I/O.
2. Interrupt- initiated I/O.
3. Direct memory access( DMA).

03/15/2025
 1. Programmed I/O: It is due to the result of the I/O instructions that are
written in the computer program. Each data item transfer is initiated by an
instruction in the program. Usually the transfer is from a CPU register and
memory. In this case it requires constant monitoring by the CPU of the
peripheral devices.Example of Programmed I/O: In this case, the I/O device
does not have direct access to the memory unit. A transfer from I/O device to
memory requires the execution of several instructions by the CPU

03/15/2025
 2. Interrupt- initiated I/O: Since in the above case we saw the CPU is kept
busy unnecessarily. This situation can very well be avoided by using an
interrupt driven method for data transfer. By using interrupt facility and
special commands to inform the interface to issue an interrupt request signal
whenever data is available from any device. In the meantime the CPU can
proceed for any other program execution.
 Note: Both the methods programmed I/O and Interrupt-driven I/O require the
active intervention of the
processor to transfer data between memory and the I/O module

03/15/2025
Direct Memory Access(DMA)
 DMA is a method that allows an I/O devices directly to or from
the main memory bypassing the CPU to speed up memory
operation.
 The process is managed by Chip know as a DMA
controller(DMAC).
 DMA Controller is a hardware device that allows I/O devices to
directly access memory with less participation of the processor.
DMA controller needs the same old circuits of an interface to
communicate with the CPU and Input/Output devices.
 It gets 4 parameters.
 1) Source Address
 2) Destination Address
 3) Byte Count
 4) Read/Write

03/15/2025
Block diagram of DMA

03/15/2025
DMA:
 Fig-1 below shows the block diagram of the DMA controller.
 The unit communicates with the CPU through data bus and control lines. Through the use of the
address bus and allowing the DMA and RS register to select inputs, the register within the DMA is
chosen by the CPU.
 RD and WR are two-way inputs. When BG (bus grant) input is 0, the CPU can communicate with DMA
registers. When BG (bus grant) input is 1, the CPU has relinquished the buses and DMA can
communicate directly with the memory.
 The DMA controller has three registers as follows.
 Address register – It contains the address to specify the desired location in memory.
 Word count register – It contains the number of words to be transferred.
 Control register – It specifies the transfer mode.

03/15/2025
DMA:
 Explanation :
 The CPU initializes the DMA by sending the given information through the data bus.
 The starting address of the memory block where the data is available (to read) or where
data are to be stored (to write).
 It also sends word count which is the number of words in the memory block to be read or
write.
 Control to define the mode of transfer such as read or write.
 A control to begin the DMA transfer.

03/15/2025
DMA:
 Bus Request : It is used by the DMA controller
to request the CPU to relinquish the control of
the buses.
 Bus Grant : It is activated by the CPU to
Inform the external DMA controller that the
buses are in high impedance state and the
requesting DMA can take control of the buses.
Once the DMA has taken the control of the
buses it transfers the data. This transfer can
take place in many ways.

03/15/2025
Serial Communication
 Serial communication is the process of sequentially transferring the
information/bits on the same channel. Due to this, the cost of wire
will be reduced, but it slows the transmission speed. Generally,
communication can be described as the process of interchanging
information between individuals in the form of audio, video, verbal
words, and written documents.
 In serial communication, binary pulses are used to show the data.
Binary contains the two numbers 0 and 1. 0 is used to show the LOW
or 0 Volts, and 1 is used to show the HIGH or 5 Volts.
 The serial communication can either be asynchronous or
synchronous.

03/15/2025
1. Synchronous Communication
 In synchronous communication, the frames or data will be constructed with the help of
combining the groups of bits. That frames will be continuously sent in time with a master
clock. It uses a synchronized clock frequency to operate the data of sender or receiver. In
synchronous communication, there is no need to use the gaps, start bits and stop bits.

03/15/2025
2. Asynchronous Communication
 In asynchronous communication, the groups of bits will be treated as an independent unit,
and these data bits will be sent at any point in time. In order to make synchronization
between sender and receiver, the stop bits and start bits are used between the data bytes.
These bits are useful to ensure that the data is correctly sent. The time taken by data bits
of sender and receiver is not constant, and the time between transmissions will be provided
by the gaps.

03/15/2025
Serial Communication
 On the basis of the data transfer rate and the
type of transmission mode, serial
communication will take many forms. The
transmission mode can be classified into
 1. simplex
 2. half-duplex
 3. full-duplex
 Each transmission mode contains the source,
also known as sender or transmitter, and
destination, also known as the receiver.

03/15/2025
1. Simplex
 In the simplex method, the data
transmission can be performed
only in one direction. At a time,
only one client (either sender or
receiver) can be active.
 Example 1:
Printers and computers are one
more example of the simplex.
Computers always send data to the
printers, but printers are not able
to send the data to the computers

03/15/2025
2. Half Duplex
 In the half-duplex, the sender and
receiver can communicate in both
directions, but not at the same
time.
 Example: Walkie-talkie is also a
classic example of half-duplex.

03/15/2025
3. Full Duplex
 In the full-duplex, the sender and the
receiver are able to send and receive at the
same time. The communication mode of full-
duplex is widely used in the world.
 Example: Audio calling or Video calling is
also an example of full-duplex.
 Telephone Network is a good example of
full-duplex mode

03/15/2025
Parallel communication
 Parallel communication is used to transmit a
huge amount of data signals simultaneously on
the different channels within the same radio path
or cable at a time.
 It is used to comprise a huge amount of wired
channels in parallel. In parallel communication,
the data transfer between sender and receiver is
done with the help of multiple channels.
 The data bus in the parallel devices is wider as
compared to the serial devices.

03/15/2025
Thank You

UNIT 5 INPUT OUTPUT.pptx computer

Recommended

More Related Content

Similar to UNIT 5 INPUT OUTPUT.pptx computer (20)

Recently uploaded (20)

UNIT 5 INPUT OUTPUT.pptx computer