1. **** demand analysis ** **

The basic requirements of the question are: in addition to the core 32-bit microcontroller, it must contain at least 1 reset button, 3 independent buttons, 2 LEDs, download interface and serial communication interface, OLED display driver, and lead to some or all IO ports. Finally, write a detection program to check whether all functions can be used normally.

The core 32-bit microcontroller can choose the STM32 series of chips produced by STMicroelectronics. Since STM32 is very popular, its related data and information are also very complete, which is conducive to the implementation of subsequent problems. This series of chips has rich registers and communication protocols, can meet various embedded openings, and can meet the core microcontroller requirements of the topic.

As we all know, the use and development of peripherals has nothing to do with the chip model they control. Therefore, we designed a development board that is compatible with different main control chips. The core board and peripheral board are combined to form a 32bit processor development board. Using the rules of STM32 packaging, a miniaturized core microcontroller PCB circuit is designed, which can be installed on different peripheral motherboards and the working environment can be changed at any time. In addition to the basic peripheral circuits of the MCU, this core microcontroller also has NAND flash memory, SDRAM, and all IO ports using BTB board-to-board connectors to facilitate the design of different functions in the future. In addition, under the same package (LQFP-144), the PCB circuit is also compatible with different series of main control chips.

2.**** Program selection and demonstration ** **

It uses the STM32 series of microcontrollers as the main control, plus NAND flash memory and SDRAM as the core board. It is equipped with network chips, audio decoding chips, serial port conversion chips, CAN communication buses and other common peripherals as peripheral development boards, which can be used for initial development. Scholars learn to use and develop DEMO materials. The circuit adopts a four-layer design, using BTB board-to-board connectors to connect the core board and peripheral board and lead out all IO ports.

It has the following advantages:

1. Four-layer boards are easy to miniaturize, and BTB will make it easier to install core boards on different motherboards for easy use and replacement.

2. Rich peripherals, which can provide learning content with different difficulty gradients for beginners.

3. The resource coordination is high and different peripherals can be combined to complete rich application functions.

3. System architecture and function description

3.1**** Core board ** **

The core microcontroller circuit design refers to the core board solution of Punctual Atom [1], and based on the reference design of the official data sheet [2], the design framework of the core board is shown in Figure 3-1 below. The main control is an STM32 series (LQFP-144 package) chip, and the basic core circuit is the main control and its peripheral circuits. In addition, there are flash memories using SPI communication, NAND flash memory and SDRAM using Parallel communication. The BTB board-to-board connector externally outputs all GPIO ports of all masters. The power supply for the circuit can come from the motherboard with BTB connection, or it can be provided by USB. USB is also connected to the STM32 port and can be used for data communication.

Figure 3-1 Framework of core microcontroller

3.2**** Peripheral Development Board ** **

Most peripherals are connected and communicated by universal standard bus interfaces or communication protocols. Therefore, when developing a peripheral board, you only need to bring out the interfaces required by different peripherals, and you can control the peripherals through the bus. The peripheral interfaces are:

SPI: Serial peripheral bus. The bus leads include SCK, MOSI, MISO and chip select lines for different devices. It has the characteristics of high-speed full-duplex. During use, multiple different devices can be connected to the same SPI bus and exchange data with different peripherals through different chip select lines, thereby improving bus communication efficiency. Peripherals that use SPI for communication include OLED displays, FLASH flash memory chips, touch screens, NRF communication chips, etc.

ETH: Ethernet communication interface, including RMII and other interfaces. After connecting the RMII interface to the PHY physical layer network card chip in the development board, network communication can be achieved by installing the LWIP protocol stack in the software.

SAI: audio transmission bus, including signal demodulation mechanisms such as PCM. You can connect the audio decoding chip with the SAI bus interface and then use the power amplifier chip to achieve audio playback. Of course, it can also cooperate with the USB FS transmission protocol to realize the USB sound card function.

CAN: Controller Area Network is an ISO internationally standardized serial communication protocol that can connect all devices that communicate through CAN, such as industrial motors, high-power electrical equipment, etc.

ADC: Analog-to-digital conversion chip, which can be used for digital collection of analog signals.

SDIO: The communication bus for SD cards and MMC and other memory cards, which can be used to build the FAFTS file system.

FMC: Flexible memory controller, which can be used to expand chip memory. FMC can also be used to control the display of the LCD. Since the LCD has its own GRAM memory, it can be abstracted into memory for reading and writing.

GPIO: General IO port, which can be used for external interrupt signal input and high and low level output, such as LED lights,

Button recognition, etc.

Figure 3-2 Overall framework of the development board

4****． Circuit Diagram and PCB ** **

4.1**** Core board ** **

The main control chip of the core board is STM32F429ZIT6. In addition to the smallest system board, it also has memory, power supply, and two LEDs.

The memory uses 32MB SDRAM, 32MB SPI communication FLASH, and 256MB NAND FLASH.

Figure 4.1 Memory circuit

Power circuit, as shown in Figure 5-1 and Figure 5-2: USB provides 5V power supply, which is connected to the U5 switching power supply chip through the F1 resettable fuse. U5-bit MP2162GQH-Z from MPS Company has a maximum input voltage of 6V and a maximum current sustainable The output is 2A, and its peripheral components are very few, which facilitates miniaturization design.

Figure 4.2 Buck circuit

The LEDs are red and green respectively.

Figure 4.3 LED circuit

4.**** 2 Peripheral Development Board****

Figure 4.4 Peripheral development board circuit 1

Figure 4.5 Peripheral development board circuit 2

The core board and peripheral development board are connected through four 30PIN BTBs, including:

1. SWD debugging port.

2. USB interface.

3. Reset button.

4. Switching step-down power supply

5. 4 reset buttons.

6. Serial port module.

7. TF card slot.

8. DS18B20 temperature sensor.

9. OLED display

10. LCD display.

11. PWM controlled MOS transistor.

12. NRF communication module.

13. CAN communication module.

14. 10/100M network port module for RMII communication.

15. PCM audio decoder.