The pin diagram of 8051 microcontroller looks as follows −. Pins 1 to 8 − These pins are known as Port 1. This port doesn’t serve 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 ...

Block Diagram Operation. Before application of clock signal, let Q 3 Q 2 Q 1 Q 0 = 0000 and apply LSB bit of the number to be entered to D in. So D in = D 3 = 1. Apply the clock. On the first falling edge of clock, the FF-3 is set, and stored word in the register is Q 3 Q 2 Q 1 Q 0 = 1000. Apply the next bit to D in. So D in = 1.