Externally Initiated Operations in Microprocessor

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

Following are the some externally initiated operations:

  1. RESET –
    This RESET key is used to clear the program counter and update with 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 chip have some pins for interrrupt 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 routine. 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 low state then the microprocessor enters into the Wait state. The Input/Output devices that are connected to microprocessor are of different speed, which is need to be synchronized with the speed of 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 communicate with the memory without interfering the processor every time.

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