MICRO PROCESSORS

What is a Microcontroller?

A Microcontroller is a programmable digital processor with necessary peripherals. Both microcontrollers and microprocessors are complex sequential digital circuits meant to carry out job according to the program / instructions. Sometimes analog input/output interface makes a part of microcontroller circuit of mixed mode(both analog and digital nature). A microcontroller can be compared to a Swiss knife with multiple functions incorporated in the same IC.

Fig. 1.1     A Microcontroller compared with a Swiss knife

Microcontrollers Vs Microprocessors

A microprocessor requires an external memory for program/data storage. Instruction execution requires movement of data from the external memory to the microprocessor or vice versa. Usually, microprocessors have good computing power and they have higher clock speed to facilitate faster computation. A microcontroller has required on-chip memory with associated peripherals. A microcontroller can be thought of a microprocessor with inbuilt peripherals. A microcontroller does not require much additional interfacing ICs for operation and it functions as a stand alone system. The operation of a microcontroller is multipurpose, just like a Swiss knife. Microcontrollers are also called embedded controllers. A microcontroller clock speed is limited only to a few tens of MHz. Microcontrollers are numerous and many of them are application specific.

Development/Classification of microcontrollers (Invisible)

Microcontrollers have gone through a silent evolution (invisible). The evolution can be rightly termed as silent as the impact or application of a microcontroller is not well known to a common user, although microcontroller technology has undergone significant change since early 1970's. Development of some popular microcontrollers is given as follows.

Intel 4004 4 bit (2300 PMOS trans, 108 kHz) 1971 Intel 8048 8 bit 1976 Intel 8031 8 bit (ROM-less) . Intel 8051 8 bit (Mask ROM) 1980 Microchip PIC16C64 8 bit 1985 Motorola 68HC11 8 bit (on chip ADC) . Intel 80C196 16 bit 1982 Atmel AT89C51 8 bit (Flash memory) . Microchip PIC 16F877 8 bit (Flash memory + ADC) .

Development of microprocessors (Visible)

Microprocessors have undergone significant evolution over the past four decades. This development is clearly perceptible to a common user, especially, in terms of phenomenal growth in capabilities of personal computers. Development of some of the microprocessors can be given as follows.

Intel 4004 4 bit (2300 PMOS transistors) 1971 Intel 8080          8085 8 bit (NMOS) 8 bit 1974 Intel 8088          8086 16 bit 16 bit 1978 Intel 80186          80286 16 bit 16 bit 1982 Intel 80386 32 bit (275000 transistors) 1985 Intel 80486 SX                      DX 32 bit 32 bit (built in floating point unit) 1989 Intel 80586     I                          MMX                          Celeron II                          III                          IV 64 bit 1993 1997 1999 2000 Z-80 (Zilog) 8 bit 1976 Motorola Power PC     601                                         602                                         603 32-bit 1993 1995