58.7.1 Debugging and 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 Ohms, not to exceed 100 Ohms with protection using Transient Voltage Suppressors (TVS), at the user’s discretion. See image below for more information.

Important: The SWCLK pin is by default internally pulled-up after reset, but a pull-up resistor on the SWLCK pin is critical for reliable operations.
Note: JTAG and Serial Wire Interface recommendations can be found in the “Basic 32-Bit MCU Design and Troubleshooting Checklist Guide” on the Microchip web site.