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Externally Initiated Operations in Microprocessor

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8085 microprocessor support some Externally initiated operations, which are also known as Peripheral operations. Different external input/output devices or signals can initiate these types of operations. In the 8085 microprocessor chip, their individual pins are assigned. 

Following are some externally initiated operations: 

  1. RESET – 
    This RESET key is used to clear the program counter and update it with the 0000H memory location. When this RESET pin is activated by any external key, then all the internal operations are suspended for that time. After that, the execution of the program can begin at the zero memory address. 
  2. Interrupt – 
    8085 microprocessor chips have some pins for interrupt like TRAP, RST 5.5, RST 6.5, and RST 7.5. The microprocessor can be interrupted from the normal instructions and asked to perform some other emergency operations, which are also known as Service routines. The microprocessor resumes its operation 
    after the completion Service routine. 
  3. READY – 
    The 8085 microprocessor has a pin called READY. If the signal at this READY pin is in a low state then the microprocessor enters into the Wait state. The Input/Output devices that are connected to the microprocessor are of different speeds, which is need to be synchronized with the speed of the microprocessor. This signal is used mainly to synchronize slower external devices with the microprocessor. 
  4. HOLD – 
    When the HOLD pin is activated by an external signal, the microprocessor relinquishes control buses and allows the external peripheral to use them. For example, the HOLD signal is used Direct memory access (DMA) data transfer. In this DMA, the external Input/Output devices are directly communicating with the memory without interfering with the processor every time.


Flexibility: Externally initiated operations allow for greater flexibility and customization in terms of the tasks that can be performed by a microprocessor. This is because external devices can provide input and output signals that can be interpreted and processed by the microprocessor to perform a wide range of tasks.

Offloading: Externally initiated operations can offload processing tasks from the microprocessor, allowing it to focus on more complex tasks. For example, input/output operations can be performed by external devices, leaving the microprocessor free to execute more complex instructions.

Reduced latency: External devices can often perform operations more quickly than the microprocessor. This can reduce latency and improve overall system performance.

Resource sharing: External devices can share resources with the microprocessor, such as memory or processing power, enabling more efficient use of system resources.


Dependency: Externally initiated operations can create a dependency on external devices, which can introduce potential points of failure. If the external device fails, the microprocessor may not be able to perform certain tasks.

Communication overhead: Communication between the microprocessor and external devices can introduce overhead, reducing overall system performance. This can be particularly problematic in real-time applications where low latency is critical.

Security: Externally initiated operations can introduce security risks, particularly if external devices are not properly secured or authenticated. Malicious actors could potentially exploit vulnerabilities in external devices to gain unauthorized access to the system.

Complexity: Externally initiated operations can introduce additional complexity into the system, requiring more advanced software and hardware design to manage and control external devices. This can increase development and maintenance costs.

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Last Updated : 07 Apr, 2023
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