I am trying to calculate the SCL clock rate given the prescaler and TWBR
The datasheet says SCL = F_CPU/(16 + 2*TWBR*Prescaler)
I am looking for 400KHz clock rate on an M644PA running at 18.432MHz. It seems as if I have to use rather low values of TWBR even at a prescaler of 1.
For a prescaler of 1, I calculate a TWBR of 15 to give a clock rate of 400,696Hz. Is this correct?
I guess I expected a larger value for TWBR and/or a larger prescaler on a CPU running this fast. It appears that there is a lot of room to slow down the TWI clock, but not much room to increase the clock especially on slower CPUs!