08-05-2012, 03:47 PM
8051 MICROCONTROLLER
8051 MICROCONTROLLER.doc (Size: 456.5 KB / Downloads: 36)
Micro controller manufacturers have been competing for a long time for attracting choosy customers and every couple of days a new chip with a higher operating frequency, more memory and upgraded A/D converters appeared on the market. However, most of them had the same or at least very similar architecture known in the world of micro controllers as “8051 compatible”. What is all this about?
The whole story has its beginnings in the far 80s when Intel launched the first series of micro controllers called the MCS 051. Even though these micro controllers had quite modest features in comparison to the new ones, they conquered the world very soon and became a standard for what nowadays is called the micro controller.
PINOUT DESCRIPTION
Pins 1-8: Port 1, each of these pins can be configured as an input or an output.
Pin 9: RS A logic one on this pin disables the micro controller and clears the contents of most registers. In other words, the positive voltage on this pin resets the micro controller. By applying logic zero to this pin, the program starts execution from the beginning.
Pins10-17: Port 3 Similar to port 1, each of these pins can serve as general input or output. Besides, all of them have alternative functions:
Pin 10: RXD Serial asynchronous communication input or Serial synchronous communication output.
Pin 11: TXD Serial asynchronous communication output or Serial synchronous communication clock output.
MEMORY ORGANISATION
The 8051 have two types of memory and these are Program Memory and Data Memory. Program Memory (ROM) is used to permanently save the program being executed, while Data Memory (RAM) is used for temporarily storing data and intermediate results created and used during the operation of the micro controller. Depending on the model in use (we are still talking about the 8051 micro controller family in general) at most a few Kb of ROM and 128 or 256 bytes of RAM are used. However…
: PROGRAM MEMORY
The first models of the 8051 micro controller families did not have internal program memory. It was added as an external separate chip. These models are recognizable by their label beginning with 803 (for example 8031 or 8032). All later models have a few Kbytes ROM embedded. Even though such an amount of memory is sufficient for writing most of the programs, there are situations when it is necessary to use additional memory as well. A typical example is so called lookup tables. They are used in cases when equations describing some processes are too complicated or when there is no time for solving them. In such cases all necessary estimates and approximates are executed in advance and the final results are put in the tables (similar to logarithmic tables).