Operations Initiated by the Microprocessor:

This basically involves communication among the MPU and peripheral devices of a microprocessor and the procedure is initiated from the MPU. Usually MPU follows the following three common sense step process while communicating with a peripheral device: first, identify the peripheral device; second, transfer the data and third, provide timing. This may be obtained with the help of three buses, viz., address bus, data bus and control bus.

MPU uses the address bus to recognize a peripheral device or a memory location. Address bus is unidirectional and has only one way of communication. They are a group of sixteen lines for an 8-bit microprocessor as 8085 and it may carry address of 216 memory locations. In a microcomputer, a binary number identifies each of the peripheral or a memory location. Address bus carries that binary address of a memory or peripheral device.

The data bus is a group of eight lines for an 8-bit microprocessor and it permit data flow in both direction (bi-directional) that means from MPU to peripheral and vice-versa. A group of eight lines may carry data from 00 (0000 0000) to FF (1111 1111).

Control bus contains single lines carrying timing signals. MPU utilizes control bus to send control signals to the peripheral device.