7.3.6 SMBus Alert Function

The TMP108 supports the SMBus alert function. When the TMP108 operates in interrupt mode (TM = 1), the ALERT pin may be connected as an SMBus alert signal. When a master senses that an alert condition is present on the ALERT line, the master sends an SMBus alert command (00011001) to the bus. If the ALERT pin is active, the device acknowledges the SMBus alert command and responds by returning its slave address on the SDA line. The eighth bit (LSB) of the slave address byte indicates whether the alert condition is caused by the temperature exceeding T_HIGH or falling below T_LOW. The LSB is high if the temperature is greater than T_HIGH, or low if the temperature is less than T_LOW. See Figure 4 for details of this sequence.

If multiple devices on the bus respond to the SMBus alert command, arbitration during the slave address portion of the SMBus alert command determines which device clears its alert status first. If the TMP108 wins the arbitration, its ALERT pin becomes inactive at the completion of the SMBus alert command. If the TMP108 loses the arbitration, its ALERT pin remains active.