37.7.1 Control A
| Name: | CTRLA |
| Offset: | 0x00 |
| Reset: | 0x00 |
| Property: | PAC Write-Protection, Write-Synchronized Bits |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| MODE | RUNSTDBY | ENABLE | SWRST | ||||||
| Access | R/W | R/W | R/W | R/W | |||||
| Reset | 0 | 0 | 0 | 0 |
Bit 7 – MODE Operating Mode
This bit defines the operating mode of the USB.
| Value | Description |
|---|---|
| 0 | USB Device mode |
| 1 | USB Host mode |
Bit 2 – RUNSTDBY Run in Standby Mode
This bit is Enable-Protected.
| Value | Description |
|---|---|
| 0 | USB clock is stopped in standby mode. |
| 1 | USB clock is running in standby mode |
Bit 1 – ENABLE Enable
Due to synchronization there is delay from writing CTRLA.ENABLE until the peripheral is enabled/disabled. The value written to CTRLA.ENABLE will read back immediately and the Synchronization status enable bit in the Synchronization Busy register (SYNCBUSY.ENABLE) will be set. SYNCBUSY.ENABLE will be cleared when the operation is complete.
This bit is Write-Synchronized.
| Value | Description |
|---|---|
| 0 | The peripheral is disabled or being disabled. |
| 1 | The peripheral is enabled or being enabled. |
Bit 0 – SWRST Software Reset
Writing a zero to this bit has no effect.
Writing a '1' to this bit resets all registers in the USB, to their initial state, and the USB will be disabled.
Writing a '1' to CTRLA.SWRST will always take precedence, meaning that all other writes in the same write-operation will be discarded.
Due to synchronization there is a delay from writing CTRLA.SWRST until the reset is complete. CTRLA.SWRST and SYNCBUSY.SWRST will both be cleared when the reset is complete.
- When the CTRLA.SWRST is written, the user must poll the SYNCBUSY.SWRST bit to know when the reset operation is complete.
- During a SWRST, access to registers/bits without the SWRST are disallowed until the SYNCBUSY.SWRST is cleared by hardware.
| Value | Description |
|---|---|
| 0 | There is no reset operation ongoing. |
| 1 | The reset operation is ongoing. |