3.4.2 USB Host/Device

The USB (Universal Serial Bus) is a hot-pluggable general-purpose high-speed I/O standard for computer peripherals. The standard defines connector types, cabling, and communication protocols for interconnecting a wide variety of electronic devices. The USB 2.0 Specification defines data transfer rates as high as 480 Mbps (also known as High Speed USB). A USB host bus connector uses four pins: a power supply pin (5V), a differential pair (D+ and D- pins) and a ground pin.

The SAM9X60-Curiosity board features three USB communication ports named USB-A to USB-C™.

The USB-A port can act only as a USB device interface and can be accessed via the USB Micro-B connector (J1).

Two resistors are placed on its power rail to form a voltage divider, converting 5V into 3.3V that is then used to signal the presence of a USB host to the MPU.

The USB-A port is used as a power source, as mentioned in Power Supply Topology and Power Distribution. In most cases, this port is limited to 500 mA.

In the case of board bring-up, USB-A is the default port used to connect to the MPU over SAM-BA (SAM Boot Assistance). For more information, refer to the product web page.

The USB-B and USB-C ports are connected to the stacked USB Type-A connector (J10) and each port can act both as device and as host.

In Host mode, the USB Host ports B and C are equipped with 500 mA high-side power switches to enable self-powered and bus-powered applications. The USBx_EN_PDxx signal controls the current limiting power switch MIC2026, which in turn supplies power to a client device. Per the USB specification, bus-powered USB 2.0 devices are limited to a maximum of 500 mA, therefore the MIC2026 limits the current and indicates an overcurrent with the USBx_OVCUR_PAxx signal. For more information about the MIC2026, refer to the product web page.