i have already read all of the links you told me

but i want to interface some 100hz and a 400khz devices, and i want all of the chips work at full speed.
when you first put CR2::CR1::CR0 bits to make the clocking signal you must enable the oscilator. the datasheet does not say what happens if you want to change the clock signal once it is functioning. do i have to initialice the pca9564 again or if i just change the CR2::CR1::CR0 bits and will it change the speed of the bus from 400khz to 100khz??