8.2.2 Connecting Multiple Devices on a Single Bus

The TMP275 features three address pins allowing up to eight devices to be connected per bus. When the TMP275 is operating in Interrupt mode (TM = 1) , the ALERT pin of the TMP275 may be connected as an SMBus Alert signal. Figure 18 shows eight TMP275 devices connected to a MCU (master) using one single bus. Each device that exists as a slave on the SMBus has one unique seven bit address, see Table 2 for TMP275 address options. When a master senses that an ALERT condition is present on the ALERT line, the master sends an SMBus Alert command (00011001) on the bus. If the ALERT pin of the TMP275 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 if the temperature exceeding T_HIGH or falling below _TLOW caused the ALERT condition. This bit will be HIGH if the temperature is greater than or equal to T_HIGH. This bit will be LOW if the temperature is less than T_LOW.

This application have eight devices connected to the bus. 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. If the TMP275 wins the arbitration, its ALERT pin becomes inactive at the completion of the SMBus Alert command. If the TMP275 loses the arbitration, its ALERT pin remains active.

Figure 18. Connecting Multiple Devices on a Single Bus