63.9.5.7 TWI Asynchronous and Partial Wakeup

The TWI module includes an asynchronous start condition detector, capable of waking the device up from a Sleep mode upon an address match (and optionally an additional data match), including Sleep modes where the TWI peripheral clock is stopped. It can also be enabled when the system is fully running. In any case, only the peripheral clock is modified and VDDCORE always remains active.

FLEX_TWI_RHR must be read before enabling the asynchronous and partial wakeup.

After detecting the START condition on the bus, the TWI will stretch TWCK until the TWI peripheral clock has started. The time required for starting the TWI peripheral depends on which Sleep mode the device is in. After the TWI peripheral clock has started, the TWI releases its TWCK stretching and receives one byte of data (client address) on the bus. At this time, only a limited part of the device, including the TWI module, receives a clock, thus saving power. If the address phase causes a TWIS address match (and optionally if the first data byte causes data match as well), the entire device is wakened and normal TWI address matching actions are performed. Normal TWI transfer then follows. If the TWI module is not addressed (or if the optional data match fails), the TWI peripheral clock is automatically stopped and the device returns to its original Sleep mode.

The TWI module has the capability to match on more than one address. The FLEX_TWI_SMR.SADR1EN/SADR2EN/SADR3EN bits enable address matching on additional addresses which can be configured through the FLEX_TWI_SWMR.SADR1/SADR2/SADR3 fields. The matching process can be extended to the first received data byte if the FLEX_TWI_SMR.DATAMEN bit is set. In that case, a complete matching includes address matching and first received data matching. The FLEX_TWI_SWMR.DATAM field can be used to configure the data to match on the first received byte.

When the system is in Active mode and the TWI enters asynchronous partial Wakeup mode, the flag SVACC must be programmed as the unique source of the TWI interrupt and the data match comparison must be disabled.

When the system exits ULP1 mode as the result of a matching condition, the SVACC flag is used to determine if the TWI is the source of the exit from ULP1 mode.