PROCESS CONTROL UNIT

8.1 MICROPROCESSOR

        The Microprocessor is a single chip very large scale integrated circuit. It consist of arithmetic logic and control circuitry and temporary registers needed for general purpose processing, control and computing. This device can fetch the instructions from memory decode it and execute them, it perform logic and arithmetic operation, accept data from input device and send the result to output device. The microprocessor has its own instruction set, which used for program the processor to do some specific task. The microprocessor performs following functions on instruction and data.

•     Receives instructions from memory
•     Receive data from input device
•     Perform computations on data as per instruction
•     Send the result of computation to storage device

    In out project microprocessor 8085 is used, which is an 8 - bit processor with 16 address line, and can address up to 64KB of memory. It has the clock speed 3 MHz.

8.2 I/O INTERFACING UNIT

    The input and output unit is connected to the processor through the I/O port.

[8255] GENERAL PURPOSE PROGRAMMABLE INTERFACE

        8255 is a programmable interface, any electronic device can be interfaced to the processor via 8255. The 8255 has three ports, port A, port B, port C. Each port can be programmed in three modes. In this project port A is configured as an output port. The port can be configured any way by writing the control word into the control register. The format of the control word for configuring the port A is given below.

Control Word Format:

bit 7	bit 6 bit 5	bit 4	bit 3	bit 2	bit 1	bit 0

MODE	MODE SELECTION (PORT A)	DIRECTION (PORT A)	DIRECTION (PORT C)	MODE SELECTION (PORT B)	DIRECTION (PORT B)	DIRECTION (PORT C)

Initializing all port as output port.

1	0	0	0	0	0	0