18F25J11 RTCC & remappable pin options

[rmteo]

but if i want to change to 100HZ i can't.. because prescale is in max (max=16) and PR2 is almost on max(max=255)..

how i could work with small frequencies?

You can't - this is a limitation of the CCP module which has only an 8-bit period register. This table is from the data sheet. With an 8MHz clock, the lowest frequency is 488Hz.