3.4.1 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 SAM9X75-Curiosity board features three USB communication ports named USB-A to USB-C™.
The USB-A port implementation on SAM9X75-Curiosity can act only as a USB device interface and can be accessed via the USB Micro-B connector (J2).
Two resistors (R1 and R2) 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 following figure shows the USB-A Port.
The following table shows the USB-A connector signal description.
| Pin No. | Signal Name | Signal Description |
|---|---|---|
| 0 | GND_USBA | Connector chassis connected to ground |
| 1 | 5V_VBUS | First port 5V power |
| 2 | USBA_N | First port data minus |
| 3 | USBA_P | First port data plus |
| 4 | ID | - (Not used) |
| 5 | GND | First port ground |
The following table shows the USB-A PIO signal description.
| PIO | Signal Name | Signal Description |
|---|---|---|
| PC08 | USBA_VBUS_DETECT_PC08 | VBUS detection |
The USB-B and USB-C ports are connected to both USB Type-A connectors (J15 and J16) and can act as hosts.
USB Host ports B and C are equipped with 500 mA high-side power switches to enable self-powered and bus-powered applications. The USBB_EN_5V_PC27 and USBC_EN_5V_PB18 signals control 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 USBB_OVCUR_PC28 and USBC_OVCUR_PC29 signals. For more information about the MIC2026, refer to the product web page.
The following figure shows the USB-B and USB-C ports.
The following table shows the USB-B and USB-C connectors signal description.
| Pin No. | Signal Name | Signal Description |
|---|---|---|
| (J15) 0 | EARTH_USB_B | Connector chassis connected to ground |
| (J15) 1 | USBB_VBUS_5V | Second port 5V power |
| (J15) 2 | USBB_N | Second port data minus |
| (J15) 3 | USBB_P | Second port data plus |
| (J15) 5 | GND | Second port ground |
| (J16) 0 | EARTH_USB_C | Connector chassis connected to ground |
| (J16) 1 | USBC_VBUS_5V | Third port 5V power |
| (J16) 2 | USBC_N | Third port data minus |
| (J16) 3 | USBC_P | Third port data plus |
| (J16) 5 | GND | Third port ground |
The following table shows the USB-B and USB-C Power Switch PIO signal description.
|
PIO | Signal Name | Signal Description |
|---|---|---|
| PC27 | USBB_EN_ 5V_PC27 | Power switch USBB enable (active high) |
| PC28 | USBB_OVCUR_PC28 | Indicates overcurrent USBB (open drain) |
| PC29 | USBC_OVCUR_PC29 | Indicates overcurrent USBC (open drain) |
| PC31 | USBC_EN_ 5V_PC31 | Power switch USBC enable (active high) |