1. What is a minimal system
The application system that can make the single chip work with the least components
2. Three elements of the minimum system
Power supply, clock circuit and reset circuit
3. Power supply
It is the VCC and GND circuit. Any electronic equipment needs power supply. When using it, pay attention to the input requirements of the power supply voltage of the single chip microcomputer, generally 3.3~5V
4. Clock circuit
The crystal oscillator is the heart of the single-chip microcomputer, without the crystal oscillator, the single-chip microcomputer cannot work normally
What is a clock circuit? There is a component called a crystal oscillator in the smallest system of a single-chip microcomputer. This component has an effect called the piezoelectric effect . What is the piezoelectric effect?
Piezoelectric effect: When some dielectrics are deformed by external forces in a certain direction, polarization will occur inside them, and at the same time, opposite charges will appear on its two opposite surfaces. When the external force is removed, it will return to the uncharged state. This phenomenon is called the positive piezoelectric effect. When the direction of the force changes, the polarity of the charge also changes. On the contrary, when an electric field is applied in the polarization direction of the dielectric, these dielectrics will also deform. After the electric field is removed, the deformation of the dielectric will disappear. This phenomenon is called the inverse piezoelectric effect.
Then, looking back at the clock circuit of the microcontroller, what is the principle. If you have played with single-chip microcomputers, you can use an oscilloscope to find that the clock circuit of the single-chip microcomputer outputs a square wave. This square wave is the clock that drives the single-chip microcomputer. The frequency of the square wave determines the speed of the single-chip microcomputer.
There is a high-gain inverting amplifier in the MCS-51 single-chip microcomputer chip. The input terminal of the inverting amplifier is XTAL1, and the output terminal is XTAL2. The oscillator circuit and clock circuit formed by this amplifier together constitute the clock mode of the single-chip microcomputer. According to the difference of the hardware circuit, the clock connection mode of the one-chip computer can be divided into the internal clock mode and the external clock mode, as shown in Figure 1.
It can be seen that the inside is an inverter, and its principle is to continuously change the voltage (polarity) at both ends of the crystal oscillator, and finally output a square wave signal. The clock of the microcontroller is determined.
5. Reset circuit
The reset circuit is a circuit used to restore the circuit to the initial state, which is equivalent to restarting the computer.
As the name suggests, the reset circuit is to reset the microcontroller. Common reset circuits are as follows:
In the reset circuit, the capacitor is connected in series with the resistor. As can be seen from the figure, when the system is powered on, the RST pin is kept at a high level first, and the time for keeping the high level is determined by the time constant RC value of the circuit. The high level of the RST pin of the microcontroller will reset for more than two machine cycles, so the reset time is maintained by calculating the RC time constant.