Did you find IIC Block Guide? See table 3-4 IIC Divider and Hold Value. Suppose you have 8MHz bus clock and you want 100kHz IIC. 8M/100k = 80. So you start looking for SCL Divider closest to 80. You may have more than one choice. There are 5 IBFD (IBC) settings for divider=80: 0x14, 0x18, 0x47, 0x4B, 0x80.
