Repeated START (Sr) Condition
Instead of the STOP condition, the master can generate a repeated START (Sr) condition. Like a START condition, to generate a repeated START condition, the master changes the SDA line from one to zero while the SCL line is HIGH (marked in red). In this case, the I2C bus remains busy. To prepare for the repeated START condition, the master sets the SDA line to one during the LOW phase of the SCL line (marked in green).
The START (S) and repeated START (Sr) conditions are functionally identical. The repeated start conditions is used in the following situations:
To continue transmission with the same slave device in the opposite direction. After the repeated START condition, the master sends the same slave device address followed by another direction bit.
To start transmission to or from another slave device. After the repeated START condition, the master sends another slave address.
To provide a READ operation from internal address. See READ Operation for details.
DLN adapters use the repeated START condition to read from the internal address (the DlnI2cMasterRead() function) and to write to and then read from the same slave device (the DlnI2cMasterTransfer() function). If a DLN adapter needs to communicate with different slaves, it finishes one transmission (with the STOP condition) and starts another transmission.