Except P0 which needs external pull-ups, rest of the ports have internal pull-ups. When 1s are
written to these port pins, they are pulled high by the internal pull-ups and can be used as
inputs. These ports are also bit addressable and so their bits can also be accessed individually.
Port P0 and P2 are also used to provide low byte and high byte addresses, respectively, when
connected to an external memory. Port 3 has multiplexed pins for special functions like serial
communication, hardware interrupts, timer inputs and read/write operation from external
memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to
operate at different baud rates. Including two timers & hardware interrupts, it has a total of
six interrupts.
2.1:- THE CIRCUIT DIAGRAM IS AS FOLLOWS