The microprocessor is a digital integrated circuit device that can be programmed with a series of instructions to perform specified functions on data. When a microprocessor is connected to a memory device and provided with a means of transferring data to and from the "outside world,"you have a microcomputer. In its basic form, a microprocessor consists of three elements : an arithmetic logic unit (ALU), a register unit, and a control unit.
The basic elements of a microprocessor.
Arithmetic .
logic S!Bi|t »ia;:a~.
unit
•U'iiMfc: *xS;a.
(ALU) .
Control.
unit.
Arithmetic Logic Unit The ALU performs arithmetic operations such as addition and subtraction and logic operations such as NOT, AND, OR, and exclusive-OR.
Register Unit During the execution of a program (series of instructions), data are temporarily stored in any of the many registers that make up this unit.
Control Unit This unit provides the timing and control signals for getting data into and out of the microprocessor, for performing programmed instructions, and for all other operations.
Microprocessor Buses.
Typically a microprocessor has three buses for information transfer internally and externally. These buses are the address bus, the data bus, and the control bus.
The Address Bus The address bus is a "one-way street" over which the microprocessor sends an address code to a memory or other external device. The size or "width" of the address bus is specified by the number of bits that it can handle. Early microprocessors had.
.
.
.
Microprocessor.
.
(Jf l)
.
"
•
•.CoirtfpVbus :.
4-bit address buses. This number has increased to 8, 16, 20, 24, and 32 bits as microprocessor technology has advanced.
The more bits there are in the address bus, the more memory locations a given microprocessor can access. With 8 bits, 256 memory locations can be accessed. With 16 bits, 65,536 memory locations can be accessed. With 32 bits, 4,295,000,000 memory locations can be accessed.
