13.20.8.1 Control A
| Name: | CTRLA |
| Offset: | 0x00 |
| Reset: | 0x00000000 |
| Property: | PAC Write-Protection, Enable-Protected, Write-Synchronized |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| DORD | CPOL | CMODE | FORM[3:0] | ||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | ||
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||
| Bit | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | |
| SAMPA[1:0] | RXPO[1:0] | TXPO[1:0] | |||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | |||
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | |||
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| SAMPR[2:0] | IBON | ||||||||
| Access | R/W | R/W | R/W | R | |||||
| Reset | 0 | 0 | 0 | 0 | |||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| RUNSTDBY | MODE[2:0] | ENABLE | SWRST | ||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | |||
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | |||
Bit 30 – DORD Data Order
This bit selects the data order when a character is shifted out from the Data register.
This bit is not synchronized.
| Value | Description |
|---|---|
| 0 | MSB is transmitted first. |
| 1 | LSB is transmitted first. |
Bit 29 – CPOL Clock Polarity
This bit selects the relationship between data output change and data input sampling in synchronous mode.
This bit is not synchronized.
| CPOL | TxD Change | RxD Sample |
|---|---|---|
| 0x0 | Rising XCK edge | Falling XCK edge |
| 0x1 | Falling XCK edge | Rising XCK edge |
Bit 28 – CMODE Communication Mode
This bit selects asynchronous or synchronous communication.
This bit is not synchronized.
| Value | Description |
|---|---|
| 0 | Asynchronous communication. |
| 1 | Synchronous communication. |
Bits 27:24 – FORM[3:0] Frame Format
These bits define the frame format.
These bits are not synchronized.
| FORM[3:0] | Description |
|---|---|
| 0x0 | USART frame |
| 0x1 | USART frame with parity |
| 0x2-0x3 | Reserved |
| 0x4 | Auto-baud - break detection and auto-baud. |
| 0x5 | Auto-baud - break detection and auto-baud with parity |
| 0x6-0xF | Reserved |
Bits 23:22 – SAMPA[1:0] Sample Adjustment
These bits define the sample adjustment.
These bits are not synchronized.
| SAMPA[1:0] | 16x Over-sampling (CTRLA.SAMPR=0 or 1) | 8x Over-sampling (CTRLA.SAMPR=2 or 3) |
|---|---|---|
| 0x0 | 7-8-9 | 3-4-5 |
| 0x1 | 9-10-11 | 4-5-6 |
| 0x2 | 11-12-13 | 5-6-7 |
| 0x3 | 13-14-15 | 6-7-8 |
Bits 21:20 – RXPO[1:0] Receive Data Pinout
These bits define the receive data (RxD) pin configuration.
These bits are not synchronized.
| RXPO[1:0] | Name | Description |
|---|---|---|
| 0x0 | PAD[0] | SERCOM PAD[0] is used for data reception |
| 0x1 | PAD[1] | SERCOM PAD[1] is used for data reception |
| 0x2 | PAD[2] | SERCOM PAD[2] is used for data reception |
| 0x3 | PAD[3] | SERCOM PAD[3] is used for data reception |
Bits 17:16 – TXPO[1:0] Transmit Data Pinout
These bits define the transmit data (TxD) and XCK pin configurations.
This bit is not synchronized.
| TXPO | TxD Pin Location | XCK Pin Location (When Applicable) | RTS | CTS |
|---|---|---|---|---|
| 0x0 | SERCOM PAD[0] | SERCOM PAD[1] | N/A | N/A |
| 0x1 | SERCOM PAD[2] | SERCOM PAD[3] | N/A | N/A |
| 0x2 | SERCOM PAD[0] | N/A | SERCOM PAD[2] | SERCOM PAD[3] |
| 0x3 |
Bits 15:13 – SAMPR[2:0] Sample Rate
These bits select the sample rate.
These bits are not synchronized.
| SAMPR[2:0] | Description |
|---|---|
| 0x0 | 16x over-sampling using arithmetic baud rate generation. |
| 0x1 | 16x over-sampling using fractional baud rate generation. |
| 0x2 | 8x over-sampling using arithmetic baud rate generation. |
| 0x3 | 8x over-sampling using fractional baud rate generation. |
| 0x4 | 3x over-sampling using arithmetic baud rate generation. |
| 0x5-0x7 | Reserved |
Bit 8 – IBON Immediate Buffer Overflow Notification
This bit controls when the buffer overflow status bit (STATUS.BUFOVF) is asserted when a buffer overflow occurs.
| Value | Description |
|---|---|
| 0 | STATUS.BUFOVF is asserted when it occurs in the data stream. |
| 1 | STATUS.BUFOVF is asserted immediately upon buffer overflow. |
Bit 7 – RUNSTDBY Run In Standby
This bit defines the functionality in standby sleep mode.
This bit is not synchronized.
| RUNSTDBY | External Clock | Internal Clock |
|---|---|---|
| 0x0 | External clock is disconnected when ongoing transfer is finished. All reception is dropped. | Generic clock is disabled when ongoing transfer is finished. The device can wake up on Receive Start or Transfer Complete interrupt. |
| 0x1 | Wake on Receive Start or Receive Complete interrupt. | Generic clock is enabled in all sleep modes. Any interrupt can wake up the device. |
Bits 4:2 – MODE[2:0] Operating Mode
These bits select the USART serial communication interface of the SERCOM.
These bits are not synchronized.
| Value | Description |
|---|---|
| 0x0 | USART with external clock |
| 0x1 | USART with internal clock |
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 Enable Synchronization Busy bit in the Synchronization Busy register (SYNCBUSY.ENABLE) will be set. SYNCBUSY.ENABLE is cleared when the operation is complete.
This bit is not enable-protected.
| Value | Description |
|---|---|
| 0 | The peripheral is disabled or being disabled. |
| 1 | The peripheral is enabled or being enabled. |
Bit 0 – SWRST Software Reset
Writing '0' to this bit has no effect.
Writing '1' to this bit resets all registers in the SERCOM, except DBGCTRL, to their initial state, and the SERCOM will be disabled.
Writing '1' to CTRLA.SWRST will always take precedence, meaning that all other writes in the same write-operation will be discarded. Any register write access during the ongoing reset will result in an APB error. Reading any register will return the reset value of the register.
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.
This bit is not enable-protected.
| Value | Description |
|---|---|
| 0 | There is no reset operation ongoing. |
| 1 | The reset operation is ongoing. |