Before proceeding to the details of how the overflowing behavior of the accumulator sets the DDS output frequency, here is a review of two important concepts. The first of these is that the FTW controls the step size between consecutive output values from the accumulator. The second factor is that the rollover point of the accumulator is set by its capacity, C, which depends on the bus width of the accumulator, N. Specifically, this capacity equals 2^N.