When operating in Host mode, the Bus Free (BFRE) bit is used to indicate an Idle bus. The host is prevented from issuing a Start condition until the BFRE bit is set, which helps to prevent collisions from other host devices that may be already active on the bus.
The Bus Free Time (BFRET) bits are used to select the amount of I2C clock cycles that determine the delay before module hardware sets the BFRE bit. The BFRET bits can be used to meet the minimum Stop hold time as defined by the I2C specification.