34.8.1 Control A

Name: CTRLA
Offset: 0x00
Reset: 0x00000000
Property: PAC Write-Protection, Enable-Protected, Write-Synchronized

Bit 3130292827262524 
  LOWTOUT  SCLSM SPEED[1:0] 
Access R/WR/WR/WR/W 
Reset 0000 
Bit 2322212019181716 
 SEXTTOEN      PINOUT 
Access R/WR/W 
Reset 00 
Bit 15141312111098 
          
Access  
Reset  
Bit 76543210 
 RUNSTDBY  MODE[2:0]ENABLESWRST 
Access R/WR/WR/WR/WR/WR/W 
Reset 000000 

Bit 30 – LOWTOUT SCL Low Time-Out

This bit enables the SCL low time-out. If SCL is held low for 25-35 ms, the client releases its clock hold, if enabled, and resets the internal state machine. Any interrupt flags set at the time of time-out remain set.

This bit is not synchronized.

ValueDescription
0Time-out disabled.
1Time-out enabled.

Bit 27 – SCLSM SCL Clock Stretch Mode

This bit controls when SCL is stretched for software interaction.

This bit is not synchronized.

ValueDescription
0SCL stretch according to Figure 34-9.
1SCL stretch only after ACK bit according to Figure 34-10.

Bits 25:24 – SPEED[1:0] Transfer Speed

These bits define bus speed.

These bits are not synchronized.

ValueDescription
0x0Standard-mode (Sm) up to 100 kHz and Fast-mode (Fm) up to 400 kHz
0x1Fast-mode Plus (Fm+) up to 1 MHz
0x2Reserved
0x3Reserved

Bit 23 – SEXTTOEN Client SCL Low Extend Time-Out

This bit enables the client SCL low extend time-out. If SCL is cumulatively held low for greater than 25 ms from the initial START to a STOP, the client releases its clock hold, if enabled, and resets the internal state machine. Any interrupt flags set at the time of time-out remain set. If the address was recognized, PREC is set when a STOP is received.

This bit is not synchronized.

ValueDescription
0Time-out disabled
1Time-out enabled

Bit 16 – PINOUT Pin Usage

This bit sets the pin usage to either two- or four-wire operation:

This bit is not synchronized.

ValueDescription
0Four-wire operation disabled
1Four-wire operation enabled

Bit 7 – RUNSTDBY Run in Standby

This bit defines the functionality in the Standby Sleep mode.

This bit is not synchronized.

ValueDescription
0Disabled – All reception is dropped.
1Wake on address match, if enabled.

Bits 4:2 – MODE[2:0] Operating Mode

These bits must be written to 0x04 to select the I2C client serial communication interface of the SERCOM.

These bits are not synchronized.

Bit 1 – ENABLE Enable

Due to synchronization, there is delay from writing CTRLA.ENABLE until the peripheral is enabled/disabled. The value written to CTRL.ENABLE reads back immediately and the Enable Synchronization Busy bit in the Synchronization Busy register (SYNCBUSY.ENABLE) is set. SYNCBUSY.ENABLE is cleared when the operation is complete.

This bit is not enable-protected.

ValueDescription
0The peripheral is disabled or being disabled.
1The peripheral is 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 is disabled.

Writing ‘1’ to CTRLA.SWRST always takes precedence, meaning that all other writes in the same write operation are discarded. Any register write access during the ongoing Reset results in an APB error. Reading any register returns 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.
Note: During SWRST, access to registers/bits without SWRST are disallowed until the hardware clears SYNCBUSY.SWRST.
ValueDescription
0There is no Reset operation ongoing.
1The Reset operation is ongoing.