8051 THEORY

   

A microcontroller is an economical computer-on-a-chip built for dealing with specific tasks, such as displaying or receiving information through LEDs or remote controlled devices. The most commonly used set of microcontrollers belong to 8051 Family. 8051 Microcontrollers continue to remain a preferred choice for a vast community of hobbyists and professionals. Through 8051, the world became witness to the most revolutionary set of microcontrollers.

Features of 8051

The main features of 8051 microcontroller are:

 i.  RAM – 128 Bytes (Data memory)

 ii. ROM – 4Kbytes (ROM signify the on – chip program space)

 iii. Serial Port – Using UART makes it simpler to interface for serial communication.

 iv. Two 16 bit Timer/ Counter

 v.  Input/output Pins – 4 Ports of 8 bits each on a single chip.

 vi.  6 Interrupt Sources

 vii.  8 – bit ALU (Arithmetic Logic Unit)

viii.  Harvard Memory Architecture – It has 16 bit Address bus (each of RAM and ROM) and 8 bit Data Bus.

  ix. 8051 can execute 1 million one-cycle instructions per second with a clock frequency of 12MHz.

This microcontroller is also called as “System on a chip” because it has all the features on a single chip. The Block Diagram of 8051 Microcontroller is as

  

Memory Architecture

The 4 discrete types of memory in 8051 are:

 i. Internal RAM – This memory is located from address 0 to 0xff.  The memory locations from 0x00 to 0x7F are accessed directly. The bytes from 0x20 to 0x2F are bit-addressable. Loading R0 and R1 the memory location from 0x80 to 0xFF can easily accessed.

 ii. Special Function Registers (SFR) – Located from address 0x80 to 0xFF of the memory location. The same instructions used for lower half of Internal RAM can be used to access SFR’s. The SFR’s are bit addressable too.

 iii. Program Memory – This is read only memory which is located at address 0. With the help of 16 bit Special Function Register DPTR, this memory can also save the tables of constants.

 iv. External Data Memory – Located at address 0. The Instruction MOVX (Move External) should be used to access the external data memory.

PIN DIAGRAM OF 8051

Applications:-

The 8051 has been in use in a wide number of devices, mainly because it is easy to integrate into a project or build a device around. The following are the main areas of focus:

i. Energy Management:Efficient metering systems help in controlling energy usage in homes and industrial applications. These metering systems are made capable by incorporating microcontrollers.

ii. Touch screens:A high number of microcontroller providers incorporate touch-sensing capabilities in their designs. Portable electronics such as cell phones, media players and gaming devices are examples of microcontroller-based touch screens.

iii. Automobiles: The 8051 finds wide acceptance in providing automobile solutions. They are widely used in hybrid vehicles to manage engine variants. Additionally, functions such as cruise control and anti-brake system have been made more efficient with the use of microcontrollers.

iv.Medical Devices:Portable medical devices such as blood pressure and glucose monitors use microcontrollers will to display data, thus providing higher reliability in providing medical results.

Various 8051 microcontrollers:-

8051 microcontrollers use two different kinds of memory such as UV- EPROM, Flash and NV-RAM. Hence 8051 will not be seen in the part number even though it is the most popular member of the 8051 family.

 i. 8751 – This microcontroller is the UV-EPROM version of 8051. This chip has only 4K bytes of UV-EPROM. It is required to have access to the PROM burner and the UV-EPROM eraser to erase the contents inside the chip before it is programmed again. The disadvantage of using this memory is the waiting time of around 20 minutes to erase the contents in order to program it again. Due to this limitation, manufacturers fabricated flash and NV-RAM versions of 8051.

 ii.  AT89C51 from Atmel Corporation – Atmel fabricated the flash ROM version of 8051 which is popularly known as AT89C51 (‘C’ in the part number indicates CMOS). The flash memory can erase the contents within seconds which is best for fast growth. Therefore, 8751 is replaced by AT89C51 to eradicate the waiting time required to erase the contents and hence expedite the development time. To build up a microcontroller based system using AT89C51, it is essential to have ROM burner that supports flash memory. Note that in Flash memory, entire contents must be erased to program it again. The contents are erased by the ROM burner. Atmel is working on a newer version of AT89C51 that can be programmed using the serial COM port of IBM PC in order to get rid of the ROM burner.