Problem:
I used a USB to TTL board to program the STC89C52RC microcontroller. I connected the board’s RX to the microcontroller’s TX (P3.1), the board’s TX to the microcontroller’s RX (P3.0), and GND to GND. After making the connections, I couldn’t download the program, and I kept receiving the prompt “Please power on the MCU.” After cold starting the microcontroller, there was still no response.
Then I tested the serial port board. When I short-circuited RX and TX on the board and sent data using another serial debugging assistant, the data appeared in the receiving window, indicating that the board seems to be functioning properly.
However, when I tested the serial port using the STC-ISP software, the sending side showed the number of transmissions, and the light on the board flashed, but there was still no data displayed in the “Receive/Keyboard Send Buffer.” I tried several versions without success.
What could be the reason? How can I successfully download the program?
PS: I believe my steps for downloading the program are correct; I’ve paid attention to the COM port and cold start. Is there anything special that needs to be set in that ISP software? Please help, I would be very grateful!!!
Answer:
Hehe, you are using the USB universal download cable, right? It has 4 (5) wires in total, with the 5 wires providing two different power voltages. You should use the 5V; connect the 5V voltage from the USB to the microcontroller’s VCC, then connect GND to the microcontroller’s GND, and finally connect TX to the microcontroller’s TXD and RXD to RXD (or connect them as you did, since some manufacturers label the pins you need to connect based on their orientation). The most important point is that when using this type of downloader, you must first disconnect VCC, then click download, and then reconnect VCC. This is equivalent to performing a cold start operation on the development board. Hope this helps; if there are any mistakes, feel free to discuss!
