Embedded Systems - 8051 Microcontroller

Brief History of 8051

The first microprocessor 4004 was invented by Intel Corporation. 8085 and 8086 microprocessors were also invented by Intel. In 1981, Intel introduced an 8-bit microcontroller called the 8051. It was referred as system on a chip because it had 128 bytes of RAM, 4K byte of on-chip ROM, two timers, one serial port, and 4 ports (8-bit wide), all on a single chip. When it became widely popular, Intel allowed other manufacturers to make and market different flavors of 8051 with its code compatible with 8051. It means that if you write your program for one flavor of 8051, it will run on other flavors too, regardless of the manufacturer. This has led to several versions with different speeds and amounts of on-chip RAM.

8051 Flavors / Members

8052 microcontroller − 8052 has all the standard features of the 8051 microcontroller as well as an extra 128 bytes of RAM and an extra timer. It also has 8K bytes of on-chip program ROM instead of 4K bytes.
8031 microcontroller − It is another member of the 8051 family. This chip is often referred to as a ROM-less 8051, since it has 0K byte of on-chip ROM. You must add external ROM to it in order to use it, which contains the program to be fetched and executed. This program can be as large as 64K bytes. But in the process of adding external ROM to the 8031, it lost 2 ports out of 4 ports. To solve this problem, we can add an external I/O to the 8031

Comparison between 8051 Family Members

The following table compares the features available in 8051, 8052, and 8031.

Feature	8051	8052	8031
ROM(bytes)	4K	8K	0K
RAM(bytes)	128	256	128
Timers	2	3	2
I/O pins	32	32	32
Serial port	1	1	1
Interrupt sources	6	8	6

Features of 8051 Microcontroller

An 8051 microcontroller comes bundled with the following features −

4KB bytes on-chip program memory (ROM)
128 bytes on-chip data memory (RAM)
Four register banks
128 user defined software flags
8-bit bidirectional data bus
16-bit unidirectional address bus
32 general purpose registers each of 8-bit
16 bit Timers (usually 2, but may have more or less)
Three internal and two external Interrupts
Four 8-bit ports,(short model have two 8-bit ports)
16-bit program counter and data pointer
8051 may also have a number of special features such as UARTs, ADC, Op-amp, etc.

Block Diagram of 8051 Microcontroller

The following illustration shows the block diagram of an 8051 microcontroller −