1. Problems arise
When I was debugging a small four-axis, I wanted to test the serial port, and then burned the f103rct6 program into the c8t6, and then I couldn't burn the program. After inspection, it should be because the PD port is turned on, but the c8t6 does not have a PD port.
2. Problem solving
First of all, my boot1 is connected to the ground with a 10k resistor. At this time, I first need to take a wire, connect the boot1 pin to 3.3v, then power on, plug in the st link, and burn the program. then it's ok