APM32 series cannot connect to the SWJ interface (SWD/JTAG).

Problem Analysis:

Possible reasons are as follows:

1. Hardware issues, such as damage to the debugger.

2. Hardware issues, such as an unstable or incorrect connection between the chip and the debugger.

3. Software issues, such as incorrect settings in the IDE software.

4. Software, read protection enabled.

5. Software issues, such as disabling the SWJ interface in the code.

6. Software issues, such as modifying the RCC, which causes PLL locking.

Solutions:

1. Hardware, damaged debugger:

-> The most direct way to determine this is by using an oscilloscope (or logic analyzer) to check if the interface-related pins have normal waveform outputs. If you don't have this equipment, you can try cross-validation by using another ARM board to attempt the connection.

2. Hardware, unstable or incorrect connection between the chip and the debugger:

-> Poor-quality DuPont wires sometimes result in poor communication waveforms, affecting normal communication. Replace them with higher-quality connection wires. Also, pay attention to the connection wire order to avoid incorrect connections.

3. Software, incorrect settings in the IDE software:

-> Open the demo in the SDK.

4. Software, read protection enabled.

5. Software, disabling the SWJ interface in the code:

6. Software, modifying the RCC and causing PLL locking:

-> If the chip has BOOT pins, you can boot the chip from SRAM first to avoid connectivity issues caused by code problems. After connecting to the chip, use an offline programmer (APM32 PROG) to erase the flash. You should be able to operate normally afterward.