Frequency Select Input. FSELECT controls which frequency register, FREQ0 or FREQ1, is used in the phase accumulator. The frequency register to be used can be selected using the FSELECT pin or the FSELECT bit. FSELECT is sampled on the rising MCLK edge. FSELECT needs to be in steady state when an MCLK rising edge occurs. If FSELECT changes value when a rising edge occurs, there is an uncertainty of one MCLK cycle as to when control is transferred to the other frequency register. To avoid any uncertainty, a change on FSELECT should not coincide with an MCLK rising edge. When the bit is being used to select the frequency register, the FSELECT pin should be tied to DGND.