31.7.1 Control A
| Name: | CTRLA |
| Offset: | 0x00 |
| Reset: | 0x00000000 |
| Property: | PAC Write-Protection, Enable-Protected Bits, Write-Synchronized Bits |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| DORD | CPOL | CPHA | 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 | |
| DIPO[1:0] | DOPO[1:0] | ||||||||
| Access | R/W | R/W | R/W | R/W | |||||
| Reset | 0 | 0 | 0 | 0 | |||||
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| IBON | |||||||||
| Access | R/W | ||||||||
| Reset | 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 shift register.
| Value | Description |
|---|---|
| 0 | MSB is transferred first. |
| 1 | LSB is transferred first. |
Bit 29 – CPOL Clock Polarity
In combination with the Clock Phase bit (CPHA), this bit determines the SPI transfer mode.
| Value | Description |
|---|---|
| 0 | SCK is low when idle. The leading edge of a clock cycle is a rising edge, while the trailing edge is a falling edge. |
| 1 | SCK is high when idle. The leading edge of a clock cycle is a falling edge, while the trailing edge is a rising edge. |
Bit 28 – CPHA Clock Phase
In combination with the Clock Polarity bit (CPOL), this bit determines the SPI transfer mode.
| Mode | CPOL | CPHA | Leading Edge | Trailing Edge |
|---|---|---|---|---|
| 0x0 | 0 | 0 | Rising, sample | Falling, change |
| 0x1 | 0 | 1 | Rising, change | Falling, sample |
| 0x2 | 1 | 0 | Falling, sample | Rising, change |
| 0x3 | 1 | 1 | Falling, change | Rising, sample |
| Value | Description |
|---|---|
| 0 | The data is sampled on a leading SCK edge and changed on a trailing SCK edge. |
| 1 | The data is sampled on a trailing SCK edge and changed on a leading SCK edge. |
Bits 27:24 – FORM[3:0] Frame Format
This bit field selects the various frame formats supported by the SPI in client mode. When the 'SPI frame with address' format is selected, the first byte received is checked against the ADDR register.
| FORM[3:0] | Name | Description |
|---|---|---|
| 0x0 | SPI_FRAME | SPI frame |
| 0x1 | - | Reserved |
| 0x2 | SPI_FRAME_WITH_ADDR | SPI frame with address |
| 0x3-0xF | - | Reserved |
Bits 21:20 – DIPO[1:0] Data In Pinout
These bits define the data in (DI) pad configurations.
In host operation, DI is MISO.
In client operation, DI is MOSI.
| DIPO[1:0] | Name | Description |
|---|---|---|
| 0x0 | PAD[0] | SERCOM PAD[0] is used as data input |
| 0x1 | PAD[1] | SERCOM PAD[1] is used as data input |
| 0x2 | PAD[2] | SERCOM PAD[2] is used as data input |
| 0x3 | PAD[3] | SERCOM PAD[3] is used as data input |
Bits 17:16 – DOPO[1:0] Data Out Pinout
This bit defines the available pad configurations for data out (DO), the serial clock (SCK) and the SPI select (SS). In client operation, the SPI select line (SS) is controlled by DOPO. In host operation, the SPI select line (SS) is either controlled by DOPO when CTRLB.MSSEN = 1, or by a GPIO driven by the application when CTRLB.MSSEN = 0.
In host operation, DO is MOSI.
In client operation, DO is MISO.
| DOPO | DO | SCK | Client SS | Host SS (MSSEN =1) | Host SS (MSSEN = 0) |
|---|---|---|---|---|---|
| 0x0 | PAD[0] | PAD[1] | PAD[2] | PAD[2] when CTRLB.MSSEN = 1, else any GPIO configured by the application | Any GPIO configured by the application |
| 0x1 | PAD[2] | PAD[3] | PAD[1] | PAD[1] when CTRLB.MSSEN = 1, else any GPIO configured by the application | Any GPIO configured by the application |
| 0x2 | PAD[3] | PAD[1] | PAD[2] | PAD[2] when CTRLB.MSSEN = 1, else any GPIO configured by the application | Any GPIO configured by the application |
| 0x3 | PAD[0] | PAD[3] | PAD[1] | PAD[1] when CTRLB.MSSEN = 1, else any GPIO configured by the application | Any GPIO configured by the application |
Bit 8 – IBON Immediate Buffer Overflow Notification
This bit controls when the buffer overflow status bit (STATUS.BUFOVF) is set when a buffer overflow occurs.
| Value | Description |
|---|---|
| 0 | STATUS.BUFOVF is set when it occurs in the data stream. |
| 1 | STATUS.BUFOVF is set immediately upon buffer overflow. |
Bit 7 – RUNSTDBY Run In Standby
This bit defines the functionality in standby sleep mode.
| RUNSTDBY | Client | Host |
|---|---|---|
| 0x0 | Disabled. All reception is dropped, including the ongoing transaction. | Generic clock is disabled when ongoing transaction is finished. All interrupts can wake up the device. |
| 0x1 | Ongoing transaction continues, wake on Receive Complete interrupt. | Generic clock is enabled while in sleep modes. All interrupts can wake up the device. |
Bits 4:2 – MODE[2:0] Operating Mode
These bits must be written to 0x2 or 0x3 to select the SPI serial communication interface of the SERCOM.
0x2: SPI client operation
0x3: SPI host operation
Bit 1 – ENABLE Enable
- This bit is write-synchronized: SYNCBUSY.ENABLE must be checked to ensure the CTRLA.ENABLE synchronization 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 CTRL.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.
- This bit is write-synchronized: SYNCBUSY.SWRST must be checked to ensure the CTRLA.SWRST synchronization is complete.
- This bit is not enable-protected.
| Value | Description |
|---|---|
| 0 | There is no reset operation ongoing. |
| 1 | The reset operation is ongoing. |