Datasheet

32.5.1 I/O Lines
The USB pins may be multiplexed with the I/O lines Controller. The user must first configure the I/O
Controller to assign the USB pins to their peripheral functions.
A 1kHz SOF clock is available on an external pin. The user must first configure the I/O Controller to
assign the 1kHz SOF clock to the peripheral function. The SOF clock is available for device and host
mode.
32.5.2 Power Management
This peripheral can continue to operate in any sleep mode where its source clock is running. The
interrupts can wake up the device from sleep modes. Events connected to the event system can trigger
other operations in the system without exiting sleep modes.
Related Links
16. PM – Power Manager
32.5.3 Clocks
The USB bus clock (CLK_USB_AHB) can be enabled and disabled in the Main Clock module, MCLK,
and the default state of CLK_USB_AHB can be found in the Peripheral Clock Masking.
A generic clock (GCLK_USB) is required to clock the USB. This clock must be configured and enabled in
the Generic Clock Controller before using the USB.
This generic clock is asynchronous to the bus clock (CLK_USB_AHB). Due to this asynchronicity, writes
to certain registers will require synchronization between the clock domains.
The USB module requires a GCLK_USB of 48 MHz ± 0.25% clock for low speed and full speed operation.
To follow the USB data rate at 12 Mbit/s in full-speed mode, the CLK_USB_AHB clock should be at
minimum 8 MHz.
Clock recovery is achieved by a digital phase-locked loop in the USB module, which complies with the
USB jitter specifications. If crystal-less operation is used in USB device mode, refer to USB Clock
Recovery Module.
Related Links
15. GCLK - Generic Clock Controller
16.6.2.6 Peripheral Clock Masking
15.6.6 Synchronization
32.5.4 DMA
The USB has a built-in Direct Memory Access (DMA) and will read/write data to/from the system RAM
when a USB transaction takes place. No CPU or DMA Controller resources are required.
32.5.5 Interrupts
The interrupt request line is connected to the Interrupt Controller. In order to use interrupt requests of this
peripheral, the Interrupt Controller (NVIC) must be configured first. Refer to Nested Vector Interrupt
Controller for details.
Related Links
11.2 Nested Vector Interrupt Controller
32.5.6 Events
Not applicable.
SAM D21 Family
USB – Universal Serial Bus
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 793