Introducing Nyquest MCU Minimum System

A single-chip minimum system or small application system refers to a system that can run on a microcontroller composed of small components. For the Nyquest MCU series, a typical mini system should include the MCU, crystal oscillator circuit, and reset circuit.

Here is the circuit diagram of the Nyquest microcontroller minimum system:

Description:

Reset circuit: It consists of a capacitor and a resistor connected in series, with the characteristic of preventing sudden changes in capacitor voltage. When the system is powered on, the RST pin will be set to a high level, and the duration of the high level depends on the RC values of the circuit. To ensure a reliable reset, the high level on the RST pin should last for at least two cycles, which can be achieved by choosing the right combination of RC values. Typically, a 10uF capacitor and an 8.2K resistor are recommended, but there are also other methods available. The main principle is to create an RC combination that generates a high level on the RST pin for a sufficient duration. For more precise calculations, you can refer to relevant books on circuit analysis.

Crystal oscillator circuit: A standard crystal oscillator circuit operates at either 11.0592MHz (for accurate 9600 and 19200 baud rates in serial communication) or 12MHz (for generating precise time intervals according to US standard for everyday use).

Crystal oscillator circuit: A standard crystal oscillator circuit operates at either 11.0592MHz (for accurate 9600 and 19200 baud rates in serial communication) or 12MHz (for generating precise time intervals according to US standard for everyday use).

MCU Part No.：NY8A062D microcontroller or other SCM compatible with the Nyquest series.

Important Note: Please be aware that for Pin 31 (EA/Vpp), if it is connected to a high level, the microcontroller will start from the internal ROM address 0000H after reset. On the other hand, if it is connected to a low level, it will start directly from the external ROM address 0000H after reset. This is an important detail that beginners tend to overlook, so please take note of this.

Reset Circuit:

Using the Reset Circuit: The reset circuit of a microcontroller acts as a reboot mechanism, much like the restart function in a computer. Just as you would press the restart button to start running the computer's internal programs from scratch after a crash, the same concept applies to single-chip microcomputers. In the event that the SCM system is running and encounters disruptions from its surroundings while executing a program, simply pressing the reset button will automatically initiate the execution of the reset button's program right from the beginning.

The Working Principle of Reset Circuit:

The reset circuit of the Nyquest MCU can be activated by connecting a high-level signal to Pin 9 for a duration of 2 microseconds. How does this process work?

In a single-chip system, the system undergoes an initial reset during startup. When a button is pressed, the system resets again. Releasing and then pressing the button will trigger another reset. Thus, controlling the reset can be achieved by toggling the button on and off while the system is running.

Why Reset during Power-On?

In the circuit diagram, the capacitor has a value of 10uF and the resistor has a value of 10k. Using this information, we can calculate that the capacitor charges to approximately 0.7 times the supply voltage (which is 5V for the microcontroller, so it reaches around 3.5V). This charging process takes about 0.1 seconds (calculated as 10k * 10uF = 0.1s).

In simpler terms, within the first 0.1 seconds after the computer starts, the voltage across the capacitor increases from 0V to 3.5V. At the same time, the voltage across the 10k resistor decreases from 5V to 1.5V (as the total voltage in a series circuit is distributed). Consequently, within 0.1 seconds, the RST pin receives a voltage ranging from 5V to 1.5V. In a properly functioning Nyquest MCU running at 5V, voltage signals below 1.5V are considered low-level signals, while signals above 1.5V are considered high-level signals. Therefore, within the first 0.1 seconds after power-on, the MCU system automatically resets (as the RST pin receives a high-level signal for approximately 0.1 seconds).

Why Reset when the Button is Pressed?

After 0.1 seconds of the SCM startup, the voltage across capacitor C gradually charges up to 5V. This is when the voltage across the 10k resistor is close to 0V and the RST pin is at a low level, allowing the system to operate normally. When the button is pressed, it opens the switch. This creates a loop across the capacitor, causing it to discharge. During the button press, the capacitor begins to release the previously stored electrical energy. As time passes, the voltage across the capacitor decreases from 5V to 1.5V or even lower within 0.1 seconds. Considering the sum of all components in the series circuit, the voltage across the 10k resistor then becomes 3.5V or higher, triggering the RST pin to receive a high-level signal once again. As a result, the SCM system automatically resets.

Conclusion:

1. The reset circuit works by providing a voltage signal higher than 2 microseconds (2US) to the RST pin of the microcontroller. If the charging and discharging time of the capacitor is longer than 2US, it triggers a reset, allowing for adjustments to the capacitance value in the circuit.

2. Pressing the button initiates a system reset. When the button is pressed, the capacitor enters a short-circuit state, discharging all the stored charge, and causing an increase in voltage across the resistor.

3.The size of the polarized capacitor C1 in the reset circuit of the Nyquest microcontroller's small system directly affects the reset time of the microcontroller. Typically, a capacitance of 10-30uF is used.

4.The small system crystal oscillator Y1 in the Nyquest microcontroller can also operate at frequencies of 6MHz or 11.0592MHz. Higher frequencies can be used under normal working conditions to enhance the microcontroller's processing speed.

5.The startup capacitors C2 and C3 in the NineQi microcontroller's small system are usually in the range of 15-33pF. It is beneficial to place these capacitors closer to the crystal oscillator, which in turn should be positioned as close as possible to the microcontroller.

6.Port P0 is an open-drain output that requires a pull-up resistor, typically with a resistance of 10k.