Hello, I'm STM8S user.
my ask is why that mcu is no operation when no connection of st-link debugger.
If i'm doing downloading the Hex file in the mcu, so mcu is operating, But ejecting the st-link debugger at the PC,
mcu is no operation.
So either you have an external pin changing the boot mode, or your code doesn't initialize something (clock, GPIO, etc) that the debugger does.
Retrieving data ...