16.7.2.1 Cold Plugging

Cold-Plugging is the detection of a debugger when the external reset is asserted (RESET pulled low). As shown in the following figure, a cold-plugging is detected when at least 3 TCK/SWCLK pin rising edges are detected while RESET is asserted. The detector state is updated upon a RESET pin rising edge. The Cold-Plugging detection is reset by a power-on reset or external reset. At startup, the TCK/SWCLK pin must be externally pulled up by 33 kΩ resistors to avoid false detection of a debugger when this pin is left unconnected on the application board. Cold-plugging detection is available once pads are correctly powered after a power-reset. If DAL.CPU0 equals 0 or 3, then Cold-Plugging is the only way to detect a debugger probe, and so the external reset timing must be longer than the power-reset timing. If external reset is de-asserted before power-reset release, the user must retry the cold-plugging procedure until it gets connected to the device.