The increment registers are readable and writable and are double-buffered to allow value changes to be made without first disabling the NCO module.
When the NCO module is enabled, the NCOxINCU and NCOxINCH registers will be written first, then the NCOxINCL register. Writing to the NCOxINCL register initiates the increment buffer registers to be loaded simultaneously on the second rising edge of the NCO_clk signal.