What is the functional block diagram and pin description of microcontroller 8051?

8051 microcontroller is a type of microcontroller designed by Intel in 1981. This microcontroller architecture is based on the Harvard architecture and was developed basically for the use in embedded systems technology. Basically this microcontroller was revised one and the updated one came into existence with CMOS technology. It is an 8-bit microcontroller.

It is built with 40 pins DIP (dual inline package), 4kb of ROM storage and 128 bytes of RAM storage, 2 16-bit timers. It contains four parallel 8-bit ports, which works as programmable and as well as addressable as per the requirement. An on-chip crystal oscillator with a frequency of 12 MHZ is inserted in the microcontroller.

Let us now discuss the architecture of 8051 Microcontroller.

In the following diagram, the system bus connects all the support devices to the CPU. As we know that CPU is the brain of any device of the microcontroller. The system bus consists of an 8-bit data bus, a 16-bit address bus and bus control signals which help in transferring data from CPU to the memory. All other devices like program memory, ports, data memory, serial interface, interrupt control, timers, and the CPU are all interact with each other through the system bus.

8051_architec

The pin diagram of 8051 microcontroller looks as follows −

8051_pin_diagram

  • Pins 1 to 8 − These pins are known as Port 1. This port does not perform any other functions. It is internally pulled up, bi-directional I/O port.
  • Pin 9 − It is a RESET pin, which is used to reset the microcontroller to its initial values.
  • Pins 10 to 17 − These pins are known as Port 3. This port helps in performing some functions like interrupts, timer input, control signals, serial communication signals RxD and TxD, etc.
  • Pins 18 & 19 − These pins are helpful for interfacing an external crystal to get the system clock.
  • Pin 20 − This pin provides the power supply to the circuit.
  • Pins 21 to 28 − These pins are known as Port 2. It functions as I/O port. Higher order address bus signals are also multiplexed using this port.
  • Pin 29 − This is PSEN pin which stands for Program Store Enable. It helps to read a signal from the external program memory.
  • Pin 30 − This is EA pin which stands for External Access input. It is used to enable/disable the external memory interfacing.
  • Pin 31 − This is ALE pin which stands for Address Latch Enable. It is used to demultiplex the address-data signal of port.
  • Pins 32 to 39 − These pins are known as Port 0. It serves as I/O port. Lower order address and data bus signals are multiplexed using this port.
  • Pin 40 − This pin is used to provide power supply to the circuit.
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