37.4.2.3 Start Condition Timing

A Start condition is initiated by either writing to the Start (S) bit (when ABD = 0) or by writing to I2CxTXB (when ABD = 1). When the Start condition is initiated, host hardware verifies that the bus is Idle, then begins to count the number of baud-divided I2CxCLK periods as determined by the Bus Free Time Status (BFRET) bits. Once the Bus Free Time period has been reached, hardware sets BFRE (BFRE = 1), the Start condition is asserted on the bus, which pulls the SDA line low, and the Start Condition Interrupt Flag (SCIF) bit is set (SCIF = 1). Host hardware then waits one full SCL period (T_SCL) before pulling the SCL line low, signaling the end of the Start condition. At this point, hardware loads the transmit shift register from either I2CxADB0/I2CxADB1 (ABD = 0) or I2CxTXB (ABD = 1).