The basic circuit of microcontroller involves powering up, crystal & resetting. To begin with connect the Pin 20 GND to ground and Pin 40 to Vcc 5 Volt. Next step is giving heart beat to microcontroller. Connect quartz crystal between Pin 18 & Pin 19. Connect 33pF capacitor across Pin 18 to GND and PIN 19 to GND. Connection is shown in the figure. Congratulate ourself as we had given life to Microcontroller
One common question asked by everyone when regains from unconscious state is “Where I am?” 8051 also asks the same question, we need to reset it. Pin 9 is RST input, when it is tied to high for more than 1 machine cycle it resets to the initial memory location. For normal execution this pin need to be connected to ground. During power on, capacitor C1 will conduct which connects Pin 9 to 5V. Once it get fully charged, it blocks DC and normal execution starts. Manual reset can be achieved by closing the switch S1 which connects Pin 9 to Vcc.
Now we need to say where our instructions are stored. Pin 31 EA Bar decides instructions are in external memory or internal memory. This pin needs to be connected to Vcc for internal memory access or GND for external memory access. Complete essential circuit is shown here. Now 8051 is perfectly ready for the mission. Almost all microcontrollers need this basic circuit for it operation.