The SAM L21 Xplained Pro has a Micro-USB connector for use with the SAM L21 USB module labeled as TARGET USB on the kit. To be able to detect when a target USB cable is connected in self-powered mode, a GPIO is used to detect the VBUS voltage on the connector. In USB host mode VBUS voltage is provided by the kit and can thus not identify a connected device, so another GPIO is used to detect the USB ID of the device.

Table 1. USB Connections
SAM L21 pin USB function Shared functionality
PA14 VBUS Detection Crystal footprint
PA24 USB D- -
PA25 USB D+ -