13.22.6.2.1 Initialization
The following registers are
enable-protected, meaning they can be written only when the I2C interface is
disabled (CTRLA.ENABLE is ‘0’):
- Control A register (CTRLA), except Enable (CTRLA.ENABLE) and Software Reset (CTRLA.SWRST) bits
- Control B register (CTRLB), except Acknowledge Action (CTRLB.ACKACT) and Command (CTRLB.CMD) bits
- Baud register (BAUD)
- Address register (ADDR) in slave operation.
When the I2C is enabled or is being enabled (CTRLA.ENABLE=1), writing to these registers will be discarded. If the I2C is being disabled, writing to these registers will be completed after the disabling.
Enable-protection is denoted by the "Enable-Protection" property in the register description.
Before the I2C is enabled it must be configured as outlined by the
following steps:
- Select I2C Master or Slave mode by writing 0x4 or 0x5 to the Operating Mode bits in the CTRLA register (CTRLA.MODE).
- If desired, select the SDA Hold Time value in the CTRLA register (CTRLA.SDAHOLD).
- If desired, enable smart operation by setting the Smart Mode Enable bit in the CTRLB register (CTRLB.SMEN).
- If desired, enable SCL low time-out by setting the SCL Low Time-Out bit in the Control A register (CTRLA.LOWTOUT).
- In Master mode:
- Select the inactive bus time-out in the Inactive Time-Out bit group in the CTRLA register (CTRLA.INACTOUT).
- Write the Baud Rate register (BAUD) to generate the desired baud rate.
- Configure the address match configuration by writing the Address Mode value in the CTRLB register (CTRLB.AMODE).
- Set the Address and Address Mask value in the Address register (ADDR.ADDR and ADDR.ADDRMASK) according to the address configuration.