MICROCONTROLLERS

HISTORY OF 8051:

               In 1976, Intel introduced its first microcontroller, 8048. It integrated the processing core with code and data memory and certain peripherals. The code memory was a 1kB mask ROM (defined by the last metallization mask during the chip processing) or EPROM (after all, Intel invented EPROM), the data memory was 64 bytes of RAM (including the 8-level stack and two pages of eight general purpose registers). Besides general-purpose I/O (see below), peripherals included a timer and an external interrupt (plus the necessary interrupt system).

                      Although the 8048 is clearly an 8-bit architecture,

                      8049 (2kB ROM/128B RAM) and

                      8050 (4kB ROM/256B RAM);

                      with ROMless versions as 8039 and 8040; and

                      8049 had also an EPROM version 8749 (the funny thing is, that 8749 came                               in 1981, one year after 8051/8751).

       In 1980, Intel introduced the successor to 8048, the 8051.

                 Intel made sure that the transition from the already successful model will be as smooth as possible. Architecturally, the 8051 is an extension to 8048. Almost every feature and resource of 8048 is present in 8051 in same or superior form. 4kB ROM and 128B RAM on chip. Pin compatibility was not maintained, but it was not a real issue. Software compatibility is not binary wise but source-wise, but that is also acceptable. The preliminary datasheet read: "Enhanced MCS-48 Architecture".

 MICROCONTROLLERS:

                Microprocessors and Microcontrollers are widely used in embedded systems products.  Microcontroller is a programmable device. A Microcontroller has a CPU in addition to fixed amount of RAM, ROM, I/O ports and a timer embedded all on single chip. The fixed amount of on-chip ROM, RAM and number of I/O ports microcontroller makes them ideal for many applications where cost and space are critical.

                 The Intel 8051 is Harvard architecture, single chip microcontroller which was developed by Intel in 1980 for use in embedded systems. It was popular in the 1980’s and early 1990’s, but today it has largely been superseded by a vast range of enhanced devices with 8051-compatible processor cores that are manufactured by more than 20 independent manufactures including Atmel, Infineon Technologies and Maxim Integrated Products.

                 8051 is an 8-bit processor, meaning that the CPU can work on only 8 bits of data at a time. Data larger than 8 bits has to be broken into 8-bit pieces to be processed by the CPU. 8051 is available in different memory types such as UV-EPROM, Flash and NV-RAM.

           The microcontroller used in this project is AT89C51. Atmel Corporation introduced this 89C51 microcontroller. This microcontroller belongs to 8051 family. This microcontroller has 128 bytes of Ram, 4K bytes of on-chip ROM, two timers, one serial port and four ports all on a single chip.AT89C51 is Flash type 8051.

          

Features of  the 805:

•   4 KB on chip program memory.
•   128 bytes on chip data memory(RAM).
•   4 reg banks.
•   128 user defined software flags.
•   8-bit data bus
•   16-bit address bus
•   32 general purpose registers each of 8 bits
•   16 bit timers (usually 2, but may have more, or less).
•   3 internal and 2 external interrupts.
•   Bit as well as byte addressable RAM area of 16 bytes.
•   Four 8-bit ports, (short models have two 8-bit ports).
•   16-bit program counter and data pointer.
•   1 Microsecond instruction cycle with 12 MHz Crystal.