34.8.5.3.1 SMBus

The I²C includes three hardware SCL low time-outs, which allow a time-out to occur for SMBus SCL low time-out, host extend time-out, and client extend time-out. This allows for SMBus functionality These time-outs are driven by the GCLK_SERCOM_SLOW clock. The GCLK_SERCOM_SLOW clock is used to accurately time the time-out and must be configured to use a 32 KHz oscillator. The I²C interface also allows for a SMBus compatible SDA hold time.

• TTIMEOUT: SCL low time of 25..35ms – Measured for a single SCL low period. It is enabled by CTRLA.LOWTOUTEN.
• TLOW:SEXT: Cumulative clock low extend time of 25 ms – Measured as the cumulative SCL low extend time by a client device in a single message from the initial START to the STOP. It is enabled by CTRLA.SEXTTOEN.
• TLOW:MEXT: Cumulative clock low extend time of 10 ms – Measured as the cumulative SCL low extend time by the host device within a single byte from START-to-ACK, ACK-to-ACK, or ACK-to-STOP. It is enabled by CTRLA.MEXTTOEN.

The SMBus-compatible logic levels are enabled by writing the SMBus Input Buffer Enable bit in Control A register (CTRLA.SMBUFEN).