6.5.5.4.3 Debugger Detection

The DSU detects the presence of the debugger and supports both hot plugging and cold plugging:

• Cold plugging detection occurs if at least three SWCLK pulses are detected before the RESET pin is de-asserted. The device must be out of Power-on Reset (POR) before these pulses can be detected.
• Hot plugging detection occurs on a falling edge of SWCLK when the part is not in Reset. An internal pull-up on SWCLK prevents false detection if SWCLK is unconnected. Hot plugging is not available when DAL = 0x0 or if the pin that SWCLK is on has been switched to a different function.

Refer to the CPU Reset Extension section for more information on hot- and cold-plugging. Once the debugger is detected, the SWDIO function takes control of the pin to which it is assigned and can only be released back for other usage by a Power-on Reset (POR) in the case of cold plugging, or by either a POR or external reset in the case of hot plugging.