Introduction to the components and functions of the microcontroller minimum system

Introduction to Microcontroller Minimum System

What is Microcontroller Minimum System

Microcontroller Minimum System refers to the simplest circuit system composed of microcontroller and external devices, which includes basic circuits such as microcontroller, crystal, power supply and reset circuit.

Microcontroller minimum system is the foundation of microcontroller development and microcontroller application. Mastering the principles and design methods of the microcontroller minimum system is of great significance for learning microcontroller programming and applications.

Composition of the microcontroller minimum system

The microcontroller minimum system consists of basic circuits such as microcontroller, crystal, power supply and reset circuit.


Microcontroller is the core of the whole system, which is a kind of integrated circuit containing functional modules such as central processing unit (CPU), memory (ROM and RAM), input/output interfaces (I/O ports), and timer counter.

Crystal oscillator

The crystal oscillator is the clock source for the operation of the microcontroller, which provides the clock signal for the microcontroller. A microcontroller needs a clock signal to synchronize its internal operations. The higher the frequency of the crystal, the faster the microcontroller will run.

Power supply

The power supply is the source of energy for the microcontroller’s smallest system, which provides the electrical power needed by the microcontroller and external devices. The power supply can be a DC or AC power source or a battery.

Reset Circuit

The reset circuit is an important part of the microcontroller’s minimum system, which is used to zero out the internal state of the microcontroller when it is powered up or reset to the initial state. The reset circuit is usually composed of a reset circuit chip, capacitors and resistors, and other devices.

Design of the microcontroller minimum system

The design of the microcontroller minimum system needs to consider the following aspects:

Selection of microcontroller

Selection of the microcontroller needs to consider the application scenarios and needs, to determine the microcontroller model and parameters. Commonly used microcontrollers are 51 series, AVR series, PIC series and so on.

Selecting a crystal

Selecting a crystal needs to consider the clock frequency and precision of the microcontroller, and generally choose a 4MHz or 8MHz crystal.

Designing the power supply

Designing the power supply needs to consider the power requirements and voltage requirements of the microcontroller and external devices, generally use 5V DC power supply.

Designing the reset circuit

Designing the reset circuit needs to consider the stability and reliability of the reset circuit, generally use the reset circuit chip and capacitors and resistors and other devices.

Operating Steps of MCU Minimum System

The operating steps of MCU minimum system are as follows:

1. Determine MCU Model and Parameters

Choose the MCU model and parameters according to the application scenarios and requirements.

2. Select crystal

Select 4MHz or 8MHz crystal according to the clock frequency and precision of the microcontroller.

3. Design the power supply

Design the 5V DC power supply according to the power demand and voltage demand of the microcontroller and external devices.

4. Design reset circuit

Design reset circuit chip and capacitor and resistor devices according to the stability and reliability of the reset circuit.

5. Connect the circuit

Connect the microcontroller, crystal, power supply and reset circuit and other devices according to the circuit diagram.

6. Write the program

Write the program and burn it into the microcontroller according to the model and parameters of the microcontroller.

7. Debugging the program

Connect the microcontroller minimum system to the computer, use the development tools for debugging, and check whether the program runs normally.

51 microcontroller minimum system?

Microcontroller minimum system, or known as the minimum application system, refers to the use of the minimum number of components composed of microcontrollers can work system. For the 51 series of microcontrollers, the minimum system should generally include: microcontroller, power supply, crystal circuit, reset circuit.

1, microcontroller

89C51 microcontroller a

2, power supply

5V DC power supply 1

3, crystal circuit

including 12MHz crystal 1, 30pF ceramic capacitors 2

4, reset circuit

10uF electrolytic capacitors 1, 4k7 resistor 1. 1 x 4k7 resistor.

The circuit is as follows:

Turn left|Turn right

Note: The /EA (pin 31) in the above figure can also be directly connected to the power supply VCC, 2k resistor can be removed.

51 microcontroller minimum system:

1, clock circuit 51 microcontroller on the clock pins: XTAL1 (19 pins): chip internal oscillator circuit input.  XTAL2 (18 feet): the chip’s internal oscillator circuit output.

2, reset circuit In the microcontroller system, the reset circuit is very critical, when the program runs (not running normally) or dead (stop running), it is necessary to reset.  MCS-5l series microcontroller reset pin RST (pin 9) appears more than 2 machine cycles of high level, the microcontroller performs a reset operation. If RST is continuously high, the microcontroller is in a cyclic reset state.

3, EA/VPP (31 pins) function and connection 51 microcontroller EA/VPP (31 pins) is the internal and external program memory selection pin. When EA stays high, the microcontroller accesses the internal program memory; when EA stays low, it only accesses the external memory regardless of whether there is an internal program memory.