Datasheet

Figure 32-2. General States

Host

CTRLA.ENABLE = 0

CTRLA.ENABLE = 1

CTRLA.MODE = 1

Device

CTRLA.ENABLE = 0

CTRLA.ENABLE = 1

CTRLA.MODE = 0

Any state

HW RESET | CTRLA.SWRST

Idle

After a hardware reset, the USB is in the idle state. In this state:

• The module is disabled. The USB Enable bit in the Control A register (CTRLA.ENABLE) is reset.

• The module clock is stopped in order to minimize power consumption.

• The USB pad is in suspend mode.

• The internal states and registers of the device and host are reset.

Before using the USB, the Pad Calibration register (PADCAL) must be loaded with production calibration

values from the NVM Software Calibration Area.

The USB is enabled by writing a '1' to CTRLA.ENABLE. The USB is disabled by writing a '0' to

CTRLA.ENABLE.

The USB is reset by writing a '1' to the Software Reset bit in CTRLA (CTRLA.SWRST). All registers in the

USB will be reset to their initial state, and the USB will be disabled. Refer to the CTRLA register for

details.

The user can configure pads and speed before enabling the USB by writing to the Operating Mode bit in

the Control A register (CTRLA.MODE) and the Speed Configuration field in the Control B register

(CTRLB.SPDCONF). These values are taken into account once the USB has been enabled by writing a

'1' to CTRLA.ENABLE.

After writing a '1' to CTRLA.ENABLE, the USB enters device mode or host mode (according to

CTRLA.MODE).

The USB can be disabled at any time by writing a '0' to CTRLA.ENABLE.

SAM D21 Family

USB – Universal Serial Bus

Datasheet Complete

DS40001882D-page 795