59.2.2 Serial Wire Debug Interface


Signal Name	Recommended Pin Connection	Description
SWCLK/TCK	Pullup (15 kΩ to 50 kΩ)⁽¹⁾ If debug mode is not required, this pin can be used as GPIO.	Serial Wire Clock / Test Clock (Boundary scan mode only) This pin is a Schmitt trigger input. No internal pullup resistor at reset.
SWDIO/TMS	Pullup (15 kΩ to 50 kΩ) ⁽¹⁾ If debug mode is not required, this pin can be used as GPIO.	Serial Wire Input-Output / Test Mode Select (Boundary scan mode only). This pin is a Schmitt trigger input. No internal pullup resistor at reset.
TDI	Pullup (15 kΩ to 50 kΩ)⁽¹⁾ If boundary mode is not required, this pin can be used as GPIO.	Test Data In (Boundary scan mode only) This pin is a Schmitt trigger input. No internal pullup resistor at reset.
TRACESWO/TDO	Floating. If boundary mode is not required, this pin can be used as GPIO.	Test Data Out (Boundary scan mode only) Output driven at up to VDDIO
JTAGSEL	In harsh environments⁽²⁾, it is recommended to tie this pin to GND if not used or to add an external low-value resistor, such as 1 kOhm.	JTAG Selection. Internal permanent pull-down resistor to GNDBU (15 kOhm). Must be tied to VDDIO to enter JTAG Boundary Scan with TST tied to VDDIO and PD0 tied to GND.

Figure 59-1. SWD Schematic Example with a 10-pin Connector

Figure 59-2. SWD Schematic Example with a 20-pin Connector

Note:

These values are given only as a typical example.
In a well-shielded environment subject to low magnetic and electric field interference, the pin may be left unconnected. In noisy environments, a connection to ground is recommended.