The system is primarily composed of a **power supply**, reset circuit, **oscillation circuit**, and expansion section. The **minimum system** schematic is illustrated in the figure below.
**Power Module**
In any complete **electronic design**, providing a stable and reliable **power supply module** is the first and most critical step. The power module serves as the foundation for the entire system’s smooth operation. Although the **51 single-chip microcontroller** has been widely used for many years, it is more sensitive to interference compared to other microcontroller series. This can lead to program errors or unexpected behavior. One effective way to prevent such issues is by ensuring that the microcontroller system is powered by a stable and well-designed power supply module.
**Power Module Circuit Diagram**
The power supply for this minimum system can be provided through the USB port of a computer or via an external 5V stable power supply. An **LED** is connected to the power circuit as an indicator, with R11 acting as a current-limiting resistor. S1 is the power switch that controls the flow of electricity to the system.
**Reset Circuit**
The purpose of the MCU's **reset circuit** is to initialize the system to a known state. During a reset, the internal registers and memory are set to predefined values, allowing the microcontroller to start from a clean slate. This process ensures that the system begins execution properly without any residual data causing errors.
The **reset circuit** typically uses a combination of a resistor and capacitor connected to the RST pin of the microcontroller. This RC network ensures that the reset signal remains active for a sufficient duration—longer than two machine cycles—to allow the microcontroller to fully reset before resuming normal operation. A common configuration uses a 10kΩ resistor and a 10µF capacitor.
There are two main types of reset: **power-on reset** and **button reset**.
1. **Power-on Reset**: When the system is first powered on, the capacitor charges through the resistor, keeping the RST pin at a high level for a short period. This allows the microcontroller to initialize correctly before returning to a low state and starting its operation.
2. **Button Reset**: This involves a push button connected in parallel with the capacitor. Pressing the button discharges the capacitor, pulling the RST pin high for a short time, which triggers a reset. This is useful for manually restarting the system.
**Oscillation Circuit**
A **crystal oscillator** is an essential component in a single-chip system. It generates the **clock frequency** required for the microcontroller to operate. The clock signal determines the speed at which the microcontroller executes instructions. The higher the frequency, the faster the processing speed.
Under normal conditions, crystal oscillators are extremely accurate, often within 50 parts per million (ppm). Some advanced crystals can be tuned using an applied voltage, known as a **voltage-controlled oscillator (VCO)**. These oscillators work by converting electrical energy into mechanical vibrations and back, ensuring a stable and precise output.
The **crystal oscillator** provides the fundamental clock signal for the microcontroller system. In many systems, all components share a single crystal to maintain synchronization. In communication systems, different frequencies may be used for the baseband and **RF signals**, but they are usually synchronized electronically.
Crystals are often used with a **phase-locked loop (PLL)** circuit to generate the required clock frequencies. If multiple subsystems need different clock signals, each can be driven by its own PLL connected to the same crystal.
The **STC89C51** microcontroller uses an **11.0592MHz crystal oscillator** as its primary clock source. Since the microcontroller includes an internal oscillation circuit, only an external crystal and two capacitors are needed. The typical capacitance values range between 15pF and 50pF, depending on the specific application requirements.
**Power Module**
In any complete **electronic design**, providing a stable and reliable **power supply module** is the first and most critical step. The power module serves as the foundation for the entire system’s smooth operation. Although the **51 single-chip microcontroller** has been widely used for many years, it is more sensitive to interference compared to other microcontroller series. This can lead to program errors or unexpected behavior. One effective way to prevent such issues is by ensuring that the microcontroller system is powered by a stable and well-designed power supply module.
**Power Module Circuit Diagram**
The power supply for this minimum system can be provided through the USB port of a computer or via an external 5V stable power supply. An **LED** is connected to the power circuit as an indicator, with R11 acting as a current-limiting resistor. S1 is the power switch that controls the flow of electricity to the system.
**Reset Circuit**
The purpose of the MCU's **reset circuit** is to initialize the system to a known state. During a reset, the internal registers and memory are set to predefined values, allowing the microcontroller to start from a clean slate. This process ensures that the system begins execution properly without any residual data causing errors.
The **reset circuit** typically uses a combination of a resistor and capacitor connected to the RST pin of the microcontroller. This RC network ensures that the reset signal remains active for a sufficient duration—longer than two machine cycles—to allow the microcontroller to fully reset before resuming normal operation. A common configuration uses a 10kΩ resistor and a 10µF capacitor.
There are two main types of reset: **power-on reset** and **button reset**.
1. **Power-on Reset**: When the system is first powered on, the capacitor charges through the resistor, keeping the RST pin at a high level for a short period. This allows the microcontroller to initialize correctly before returning to a low state and starting its operation.
2. **Button Reset**: This involves a push button connected in parallel with the capacitor. Pressing the button discharges the capacitor, pulling the RST pin high for a short time, which triggers a reset. This is useful for manually restarting the system.
**Oscillation Circuit**
A **crystal oscillator** is an essential component in a single-chip system. It generates the **clock frequency** required for the microcontroller to operate. The clock signal determines the speed at which the microcontroller executes instructions. The higher the frequency, the faster the processing speed.
Under normal conditions, crystal oscillators are extremely accurate, often within 50 parts per million (ppm). Some advanced crystals can be tuned using an applied voltage, known as a **voltage-controlled oscillator (VCO)**. These oscillators work by converting electrical energy into mechanical vibrations and back, ensuring a stable and precise output.
The **crystal oscillator** provides the fundamental clock signal for the microcontroller system. In many systems, all components share a single crystal to maintain synchronization. In communication systems, different frequencies may be used for the baseband and **RF signals**, but they are usually synchronized electronically.
Crystals are often used with a **phase-locked loop (PLL)** circuit to generate the required clock frequencies. If multiple subsystems need different clock signals, each can be driven by its own PLL connected to the same crystal.
The **STC89C51** microcontroller uses an **11.0592MHz crystal oscillator** as its primary clock source. Since the microcontroller includes an internal oscillation circuit, only an external crystal and two capacitors are needed. The typical capacitance values range between 15pF and 50pF, depending on the specific application requirements.16000mAh Fast Charging Battery
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