MICROPROCESSOR
WHAT IS A MICROPROCESSOR?
computer, large or small, can be represented functionally (in a simplified form) by the blockdiagram in Figure. 1.1. As shown, it comprises of three basic parts or sub-systems :
1. CENTER PROCESSING UNIT (CPU)
It performs the necessary arithmetic and logic operations and controls the timing and general operation of the complete system.
2. INPUT / OUTPUT (I/O) DEVICES
Input devices are used for feeding data into the CPU, examples of these devices are toggle switches, analog-to-digital converters, paper tape readers, card readers, keyboards, disk etc. The output devices are used for delivering the results of computations to the outside world; examples are light emitting diodes, cathode ray tube (CRT) displays, digital-to-analog converters, card and paper-tape punches, character printers, plotters, communication lines etc. The input-output subsystem thus allows the computer to usefully communicate with the outside world. Input-output devices are also called as peripherals.
3. Memory
It stores both the instructions to be executed (i.e., the program) and the data involved. It usually consists of both RAMs (random-access memories) and ROMS (read-only memories). A microprocessor is an integrated circuit designed to function as the CPU of a microcomputer.
WHAT IS INSIDE A MICROPROCESSOR ?
The microprocessor or CPU reads each instruction from the memory, decodes it and executes it. It processes the data as required in the instructions. The processing is in the form of arithmetic and logical operations. The data is retrieved from memory or taken from an input device and the result of processing is stored in the memory or delivered to an appropriate output device, all as per the instructions. To perform all these functions, the μP (microprocessor) incorporates various functional units in an appropriate manner. Such an internal structure or organizational structure of μP, which determines how it operates, is known as its architecture.
A typical microprocessor architecture :
1. BUSSES
μC (microcomputer), like all computers, manipulates binary information. The binary information is represented by binary digits, called bits. μC operates on a group of bits which are referred to as a word. The number of bits making- μP a word varies with the μP. Common word sizes are 4, 8, 12 and 16 bits (μPs with 32 bit-word have also of late entered the market). Another binary terms that will be of interest in subsequent discussions are the byte and the nibble, which represent a set of 8 bits and 4 bits, respectively.
2. Arithmetic Logical Unit (ALU)
The arithmetic-logic unit is a combinational network that performs arithmetic and logical operations on the data.
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