3.18.1 USB 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 USBA port implementation on the SAM9X75 cHybrid can act only as a USB device interface and can be accessed via the USB Type-C® connector (J1).
Two resistors (R1 and R2) are placed on its power rail to form a voltage divider, converting 5V into 3.3V, which is then used to signal the presence of a USB host to the MPU.
The USBA 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, USBA 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 following figure shows the USBA port.
| Pin Name | Signal Name | Signal Description |
|---|---|---|
| VBUS | 5V_VBUS | First port 5V power |
| D- | USBA_N | First port data minus |
| D+ | USBA_P | First port data plus |
| CCx pins | ID | Connected with a 5.1K pull-down resistor: this selects the maximum current possible without negotiation from the power delivery host |
| GND | GND | First port ground |
| Shield | GND_USBA | Connector chassis connected to ground |
The following table provides the USBA PIO signal description.
| PIO | Signal Name | Signal Description |
|---|---|---|
| PC08 | USBA_VBUS_DETECT_PC08 | VBUS detection |