STC8 Learning Board

As a learning board, its functions are shown in the figure below. It includes essential modules for beginners in 51 microcontrollers.
Here are some points to note in circuit design
: 1. Please select a 10uF decoupling capacitor for CH340 (instead of the 100nF commonly used in many schematics; this may also be a problem with my circuit). Otherwise, the computer will not be able to recognize the USB device.
2. CH340's RXD and TXD correspond to the MCU's TXD and RXD. Also, to ensure STC chip cold start, a small resistor needs to be connected in series on the CH340's RXD pin, and a diode in series on the TXD pin. Otherwise, CH340 will supply power to the chip and energize VCC. Actual measurements show that without the resistor and diode, VCC is approximately 3V (power supply is 5V).
3. For the Type-C interface design, please follow the official documentation specifications (CC1 and CC2 must be connected to a 5.1kΩ resistor before grounding, DP and DN must be connected to a 33Ω resistor before connecting to CH340).
Experts in the technical group generally believe that the resistors on CC, DP, and DN are unimportant in low-speed circuits, but should be included in high-speed circuits. However, I once saw a Bilibili user say, "Type-C can still be used without a resistor connected to the CC pin; that's a blessing from Type-C." This shows that you still have to follow the official documentation, otherwise you might make mistakes.
Some points to note in my circuit design
: 1. Since the STC8H8K64U chip does not have P1.2, I used P5.2 as P1.2. When writing the program, pay attention to this.
Taking the AD conversion code as an example, the following code can be used to read data:
adval=P1&(0xFB|P5);
2. When using port P3.6, set it to weak pull-up, and P4.2 to high impedance input; when using port P4.2, set it to weak pull-up, and P3.6 to high impedance input; when using port P3.7, set it to weak pull-up, and P4.4 to high impedance input; when using port P4.4, set it to weak pull-up, and P3.7 to high impedance input.
3. To ensure the buzzer power, the GPIO controlling the active buzzer should be set to push-pull output. The default quasi-bidirectional port's drive capability is insufficient.
The port operating mode configuration is as follows:
4. The DAC0832 outputs current. To observe the change in output current, please use a red LED. Do not use green or blue LEDs, as these require a larger current to light, and the DAC0832 may not be able to drive them.
5. Program Download: With the chip powered off, import the generated hex file into the STC program download software, click "Download/Programming," and then power on the chip. The chip will complete the program download while powered on.
Some attached
instructions include: Sample Program.rar; Partial Case Program I wrote;
STC8H8K64U-STC89-DEMO-CODE-20230116.rar; Official STC-Dog-Beating Stick Series Core Experiment Board Case Program
Basic Module Program.rar; Guo Tianxiang 51 Microcontroller Learning Board Accompanying Case Program;
STC8 Introduction Manual.pdf; STC8 Series Microcontroller Technical Reference Manual. For
demonstration videos, please refer to the Bilibili video: [STC8 Learning Board Case Demonstration]. https://www.bilibili.com/video/BV1z7bCeHEuM/?share_source=copy_web&vd_source=1cc6752786a7dd940c6c809a85212bba
 
Finally, I sincerely request that all experts leave their valuable opinions.