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MPU Communication in Computer Organization

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MPU communicates with the outside world with the help of some external devices which are known as Input/Output devices. The MPU accepts the binary data from input devices such as keyboard and analog/digital converters and sends data to output devices such as printers and LEDs. For performing this task, MPU first need to identify the input/output devices. There are two different methods by which I/O devices can be identified: Using 8-bit address, and Using 16-bit address. These methods are described briefly in the following sections:

  1. I/Os with 8-bit addresses – This is also known as peripheral-mapped I/O or I/O-mapped-I/O. In this type of I/O, MPU uses eight address lines to identify an input or an output devices. This is an 8-bit numbering system for I/Os used in conjunction with the input and output instructions. This is also known as I/O space that is separate from the memory space which is 16-bit numbering system. The eight address lines have 2^8 combinations which is total 256 addresses; therefore MPU can identify 256 input devices and 256 output devices with addresses ranging from 00H to FFH. The input and output devices can be differentiated by using the control lines I/O Read and I/O Write. MPU uses I/O Read control signal for input devices and I/O Write control signal for output devices. The individual addresses of I/O Map is known as I/O port numbers. These I/O devices cannot be connected directly to the data bus or the address bus; all connections must be made through tri-state interfacing devices so they will enabled and connected to the buses only when the MPU chooses to communicate with them.
  2. I/Os with 16-bit addresses – This is also known as Memory-mapped I/O. In this type of I/O, MPU uses sixteen address lines to identify an input or an output devices; an I/O is connected as if it is a memory register. The MPU uses same control signal (Memory Read and Memory Write) and instructions as those of memory. In some microprocessors, such as the Motorola 6800, all I/Os have 16-bit addresses; I/Os and memory share the same memory map (64K). The steps in communicating with an I/O device are similar for both 8-bit and 16-bit addresses. The steps are summarized below:
    1. The MPU places an 8-bit address ( or 16-bit address) on the address bus, which is decoded by external decode logic.
    2. The MPU sends a control signal (I/O Read or I/O Write) and enables the I/O device.
    3. Data are transferred using the data bus.

Table: Comparison of 8-bit and 16-bit Address I/O Mapping

Features 8-bit I/O Mapping  16-bit I/O Mapping
Number of Address Lines  16
Total I/O Devices  256 65536
Address Range  00H to FFH  0000H to FFFFH
Control Signals  I/O Read and I/O Write  I/O Read and I/O Write
Interfacing Devices Required  Yes No
Memory and I/O Sharing  No Yes



Efficient data transfer: MPU communication can provide fast and efficient transfer of data between multiple devices in a computer system.
Scalability: MPU communication allows for easy scalability, as additional devices can be added to the system without affecting the performance of the existing devices.
Distributed processing: MPU communication allows for distributed processing, where different processors can work on different parts of a task simultaneously.
Reduced data loss: MPU communication can help to reduce the loss of data during transmission, as error-checking and correction mechanisms can be implemented.


Complexity: MPU communication can be complex to implement, as it requires the use of specialized hardware and software.
Latency: MPU communication can introduce latency or delay in data transmission, which can affect the overall performance of the system.
Compatibility : Different devices may use different communication protocols or standards, which can create compatibility issues when trying to communicate between them.
Security concerns: MPU communication can potentially pose security risks if data is intercepted or accessed by unauthorized parties.

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Last Updated : 14 May, 2023
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