3.3.2. Internal Coefficient and Pre-Adder for Fixed-Point Arithmetic
When you enable input register for the pre-adder feature, these input registers must have the same clock setting.
The input cascade support is only available for 18-bit mode when you enable the pre-adder feature.
In both 18-bit and 27-bit modes, you can use the coefficient feature and pre-adder feature independently.
When internal coefficient feature is enabled in 18-bit modes, you must enable both top and bottom coefficient.
When pre-adder feature is enabled in 18-bit modes, you must enable both top and bottom pre-adder.