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Peripheral device, I/O interface

Program: B.Tech (CSE)

Course: Computer Architecture and Organization

• (^) Peripheral Devices
• (^) Input-Output Interface
• (^) Asynchronous Data Transfer
• (^) Modes of Transfer
• (^) Priority Interrupt
• Direct Memory Access

INPUT-OUTPUT ORGANIZATION

INPUT/OUTPUT INTERFACE

• (^) Provides a method for transferring information between internal storage (such

as memory and CPU registers) and external I/O devices

• (^) Resolves the differences between the computer and peripheral devices
  • (^) Peripherals - Electromechanical Devices
  • (^) CPU or Memory - Electronic Device
  • (^) Data Transfer Rate
    • (^) Peripherals - Usually slower
    • (^) CPU or Memory - Usually faster than peripherals
      • (^) Some kinds of Synchronization mechanism may be needed Unit of Information
• Peripherals – Byte, Block, …
• (^) CPU or Memory – Word
  • (^) Data representations may differ

I/O BUS AND INTERFACE MODULES

Each peripheral has an interface module associated with it

Interface

• Decodes the device address (device code)
• Decodes the commands (operation)
• Provides signals for the peripheral controller
• Synchronizes the data flow and supervises the transfer rate between peripheral and CPU or Memory

Typical I/O instruction

(Command)

Op. code (^) Device address Function code

Processor

Interface

Keyboard and display terminal

Magnetic Printer tape

Interface Interface Interface

Data Address Control

Magnetic disk

I/O bus

I/O BUS AND MEMORY BUS

• MEMORY BUS is for information transfers between CPU and the MM

• I/O BUS is for information transfers between CPU and I/O devices through their I/O interface

• Many computers use a common single bus system for both memory and I/O interface units

• Use one common bus but separate control lines for each function
• Use one common bus with common control lines for both functions

• Some computer systems use two separate buses, one to communicate with memory and the other with I/O interfaces

• Communication between CPU and all interface units is via a common I/O Bus
• An interface connected to a peripheral device may have a number of data registers , a control register , and a status register
• A command is passed to the peripheral by sending to the appropriate interface register
• Function code and sense lines are not needed (Transfer of data, control, and status information is always via the common I/O Bus)

Functions of Buses

Physical Organizations

I/O Bus

ISOLATED vs MEMORY MAPPED I/O

• Separate I/O read/write control lines in addition to memory read/write control lines
• Separate (isolated) memory and I/O address spaces
• Distinct input and output instructions

Isolated I/O

Memory-mapped I/O

• A single set of read/write control lines (no distinction between memory and I/O transfer)
• Memory and I/O addresses share the common address space -> reduces memory address range available
• No specific input or output instruction -> The same memory reference instructions can be used for I/O transfers
• Considerable flexibility in handling I/O operations

Input/Output Interfaces

References

• Morris Mano, “Computer System

Architecture”, Pearson Education, 3rd

edition.