Chapter 2
INTRODUCTION OF 8051 MICRO CONTROLLERS
Intel 8051 is a single chip microcontroller designed in Harvard infrastructure manner. It
was established in 1980 by the Intel. It is developed to use in the embedded systems. In today’s
days it become very popular and many devices use this chip. Now these chips are manufactured
by many companies like Siemens AG, NXP, Novato, Silicon Laboratories, Cypress
Semiconductor, Atmel and ST Microelectronics. The integrated version of 8051 is MCS 51.
2.1 Memory Architecture:
There are four types of memory in 8051 microcontroller chip namely the internal
memory RAM, external sata memory, program memory and function registers. The IRAM or
internal Ram has the address ranging from 0 to 0xFF. IRAM can access the memory of 0x00 to
0x7F directly. It can also access the bytes ranging from 0x20 to 0x30. The address from 0x80 to
0xFF should eb addressed indirectly by the IRAM. They can be accessed using @R1 and @R0
syntax. Input the address in place of “R”.
The address of XRAM or external RAM also start with 0. It can be on – off chip and thus
addresses are accessed using the MOVX instruction. Numerous types of 8051 contains the 256
bytes of IRAM and few kB of XRAM. The XRAM can also be disabled and then every MOVX
instruction will be fetched from the external bus.
2.2 Programming:
8051 contains high level language compiler in it and thus high level language program
code can be executed in these microcontrollers. The most frequent use compiler is the C

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