2.4 Debugging or Programming Pins
The SWDIO, SWO, SWCLK pins are used for In-Circuit programming and debugging purposes. It is recommended to keep the trace length between the debug external connector and the debug pins on the device as short as possible to minimize ESD/EMI vulnerabilities. If the debug external connector is expected to experience an ESD event, a series resistor is recommended, with the value in the range of a few tens of Ωs, not to exceed 100 Ωs with protection using Transient Voltage Suppressors (TVS), at the user’s discretion. Refer to the Schematic Checklist chapter.