The Intel 8051 is a microcontroller developed by Intel in 1980 for use in embedded products and still (2003) one of the most popular microcontrollers. The 8051/8031 cores are used in over 100 devices from more than 20 independent manufacturers such as Dallas, Philips and Atmel.
The microcontroller is based on a Harvard architecture and although originally designed for single chip microcontroller applications an expanded mode allows a full 64K of external ROM and 64K of external RAM to be addressed by means of separate chip selects for program and register access.
A particular feature of the 8051 microcontroller was the inclusion of a boolean processing engine which allowed bit operations to be carried out directly and efficiently on internal registers and RAM. This led to the 8051 being popular in industrial control applications and it was widely used in early programmable logic controller designs.
The 8051 was also used in the keyboard of the first IBM PC, where it converted keypresses into the serial data stream which is sent to the main unit of the computer. The 8051 and derivatives have remained the de_facto standard for PC keyboards over the years and are still used today (2004) for basic model keyboards.
The 8052 is an enhanced version of the 8051 that features:
256 bytes of internal RAM, instead of 128
a third 16_bit timer
additional Special Function Registers to support the third timer
The 8051 was one of the first microcontroller families, and remains one of the most commonly used.
The 8051 family was created by Intel, but is now largely driven by other companies, including Atmel, Dallas Semiconductor, and Philips.
Myke Predko is the author of "Programming and Customizing the 8051 Microcontroller", and the 8051 section of his web site is filled with 8051 resources, including info on the book, an RTOS, math functions, code snippets, and links to other 8051 books and resources.
During execution of an LJMP, the 8051 replaces the contents of its 16-bit PC with the second and third bytes of the LJMP instruction.
This bit, A15, is output by the 8051 on its P2.7 pin.
It consists of an 8051 instruction sequencer and decoder, the three-bit XAR and associated logic, a local stack to save and restore the XAR on calls/interrupts and returns, an instruction translation circuit in the data path, synchronization circuits, address latches, and various input and output buffers.
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