Description   Atmel AT89C51 Microcontroller is an 8-bit microcontroller. it belongs to Atmel’s 8051 families. It has 4 KB of flash and this flash is programmable. It has 128 bytes of RAM.  We can be erased and program the flash almost 1000 times.  In 40 pin Atmel 89C51 IC there are four ports as P1, P2, P3, P0. All ports are 8 bit bidirectional. These ports used as input and output ports. It is connected to external memory, P0 needs pull-ups resistance. P0 and P2 are used to provide low byte and high byte addresses.AT89C51 has serial communication with built-in UART. it has also different baud rate and it can be programmed according to it. it has two timers. It also has hardware interrupts. Total it has 6 interrupts. Features:  High voltage capable = noMaximum operating  voltage of ATmel= 5.5VMinimum Operating Voltage of AT89C51 = 4VMaximum operating Temperature of Microcontroller  = -55C to 125CNumber of UART module Atmel Microcontroller = 1Number of 16-bit Timers of Atmel AT89C51 Microcontroller = 2Number of comparators = 2Maximum CPU Speed = 24RAM capacity = 128Program Memory Size = 4K FlashArchitecture = 8051CPU = 8 bits 8051Specifications of Atmel AT89C51: It is used in Arduino.4KB Flash Bytes8 bit CPU6.6 Maximum Operating Voltage0 to 24 Hz Maximum Oscillating frequency128 x 8 bit internal RAM32 lines of I/OTwo counters of 16 Bits