Microprocessor and Computer Architecture

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Input – Output Interface

Here is the explanation of Input – Output Interface:

An input-output interface is a system or component that facilitates communication between a computer or electronic device and external devices or users.

•Its primary function is to manage the flow of data between these devices or users and the computer system.

•They provide a method for transferring information between internal system and input-output devices.

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•In micro-computer base system, the only purpose of peripheral devices is just to provide special communication links for the interfacing them with the CPU.

•To resolve the differences between peripheral devices and CPU, there is a special need for communication links.

The major differences are as follows:

→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 also a synchronization mechanism because the data transfer rate of peripheral devices are slow than CPU.

→In peripheral devices, data code and formats are differ from the format in the CPU and memory.

→The operating mode of peripheral devices are different and each may be controlled so as not to disturb the operation of other peripheral devices connected to CPU.

  • Interface is a shared boundary between the processor bus and the peripheral device.
  • Data Transfer: It facilitates the transfer of data between the CPU, memory, and peripheral devices such as hard drives, USB devices, graphics cards, and network interfaces.
  • Address Bus and Data Bus: The I/O bus typically consists of an address bus for specifying the target device and a data bus for transmitting the actual data.
  • Bus Speed: The speed of data transfer on the I/O bus is an important factor in determining the overall performance of a computer system.

Interface modules act as intermediary components that enable communication between different hardware components or systems that may use different communication protocols.

Key Points:

  • Adaptation: Interface modules provide a way for devices with different electrical, mechanical, or communication characteristics to work together seamlessly.
  • Standardization: They often adhere to industry standards, allowing devices from different manufacturers to be compatible with each other.
  • Examples: USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), PCIe (Peripheral Component Interconnect Express), and SATA (Serial ATA) are examples of interface standards used in computers.
  • Expansion Cards: Some interface modules take the form of expansion cards that can be inserted into slots on the motherboard to provide additional functionality, such as graphics cards, network adapters, or sound cards.
types of command

Let’s briefly explain each of the commands you mentioned:

  • Example: In the case of a disk drive, an I/O command might instruct the drive to read or write data.
  • Example: For a printer, a control command could be used to set the print quality, paper size, or other operational parameters.
  • Example: The CPU might send a status command to a printer to check if it is ready to accept a print job.
  • Example: In the context of a display, a data output command could be used to send pixel data to the monitor for visual representation.
  • Example: When a keyboard receives input from a user, a data input command is generated to transfer that input data to the CPU for processing.
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  •  Data Bus Buffer : The bus buffer use bi-directional data bus to communicate with CPU. All control word data and status information between interface unit and CPU are transferred through data bus. 
  • Port A and Port B : Port A and Port B are used to transfer data between Input-Output device and Interface Unit. Each port consist of bi-directional data input buffer and bi-directional data output buffer. Interface unit connect directly with an input device and output disk or with device that require both input and output through Port A and Port B i.e. modem, external hard-drive, magnetic disk. 
  • Control and Status Register : CPU gives control information to control register on basis of control information. Interface unit control input and output operation between CPU and input-output device. Bits which are present in status register are used for checking of status conditions. Status register indicate status of data register, port A, port B and also record error that may be occur during transfer of data. 
  • Read/Write Control Logic : This block generates necessary control signals for overall device operations. All commands from CPU are accepted through this block. It also allow status of interface unit to be transferred onto data bus through this block accept CS, read and write control signal from system bus and S, S1 from system address bus. Read and Write signal are used to define direction of data transfer over data bus.
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The read signal direct data transfer from interface unit to CPU and write signal direct data transfer from CPU to interface unit through data bus. Address bus is used to select to interface unit. Two least significant lines of address bus ( A, A1 ) are connected to select lines S0, S1. This two select input lines are used to select any one of four registers in interface unit. The selection of interface unit is according to the following criteria :

Chip SelectOperationSelect linesSelection of Interface unit
00100Port A
00101Port B
00110Control Register
00111Status Register
Chip SelectOperationSelect linesSelection of Interface unit
01000Port A
01001Port B
01010Control Register
01011Status Register
  • If S0, S1 = 0 1, then Port B data register is selected for data transfer between CPU and I/O device.
  • If S0, S1 = 1 0, then Control register is selected and store the control information send by the CPU.

An I/O bus, also known as Input/Output bus, is a communication system used in a computer or similar device to transfer data between the CPU (Central Processing Unit), memory, and peripheral devices such as keyboard, mouse, printers etc.

  • The I/O bus, or Input/Output bus, handles communication between the CPU and peripheral devices such as hard drives, graphics cards, network adapters, USB devices, etc.
  • It provides a pathway for data to move between the CPU and peripherals.
  • Unlike the memory bus, which primarily deals with transferring data to and from RAM, the I/O bus deals with a diverse range of devices, each with its own data transfer requirements and protocols.
  • I/O buses often have a wider variety of speeds and protocols compared to memory buses, as different peripherals may have different data transfer needs.

A memory bus is a communication pathway used specifically for transferring data between the CPU (Central Processing Unit) and the main memory (RAM – Random Access Memory) in a computer system.

  • The memory bus is responsible for communication between the CPU and the computer’s memory subsystem (RAM).
  • It facilitates the transfer of data and instructions between the CPU and RAM.
  • The memory bus is typically optimized for high-speed, low-latency transfers, as quick access to memory is crucial for efficient operation.
  • Modern memory buses often use technologies like DDR (Double Data Rate) to maximize throughput.

Isolated I/O is the method used in computer system to communicate with external devices , such as peripherals or other hardware components.

  • In isolated I/O, the CPU communicates with external devices by using specific input and output instructions. These instructions are designed to transfer data between the CPU and the external device.
  • When using isolated I/O, special commands are used to transfer data to or from specific ports or memory locations dedicated to the external device.
  • Isolated I/O requires explicit instructions to read from or write to the device, making it more controlled and precise.
  • The communication between the CPU and the external device occurs via a dedicated set of I/O instructions, which may include IN (input) and OUT (output) instructions in assembly language.

Memory – Mapped I/O is the method used in computer system to communicate with external devices , such as peripherals or other hardware components.

  • In memory-mapped I/O, the external device is mapped to the memory address space of the CPU. This means that the CPU accesses the external device by reading from or writing to specific memory addresses reserved for the device.
  • Memory-mapped I/O allows the CPU to interact with the external device in a similar way it interacts with memory, using load and store instructions.
  • The advantage of memory-mapped I/O is that it simplifies the programming model, as devices are accessed using memory read and write operations rather than specific I/O instructions.
  • Memory-mapped I/O can lead to more efficient data transfers since it leverages the CPU’s existing memory access mechanisms.
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