The TMP43x are SMBus interface-compatible. In SMBus protocol, the device that initiates the transfer is called a master, and the devices controlled by the master are slaves. The bus must be controlled by a master device that generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions.
To address a specific device, a START condition is initiated. START is indicated by pulling the data line (SDA) from a high to low logic level when SCL is high. All slaves on the bus shift in the slave address byte, with the last bit indicating whether a read or write operation is intended. During the ninth clock pulse, the slave being addressed responds to the master by generating an Acknowledge and pulling SDA low.
Data transfer is then initiated and sent over eight clock pulses followed by an Acknowledge bit. During data transfer SDA must remain stable when SCL is high because any change in SDA when SCL is high is interpreted as a control signal.
When all data are transferred, the master generates a STOP condition. STOP is indicated by pulling SDA from low to high when SCL is high.