18.4.2.3.4 Auto Shift of Filter Output

The processing capacity of the filter is limited to 32 bits. Depending on the size of the input values, this limit can be exceeded and will cause incorrect filter operation. It is the user’s responsibility to ensure that the size of input values, filter length (decimation ratio) and filter order do not exceed 32 bits, complying with the constraint given by Equation 18-8.

$Input\_bits+length\_bits\times order\le 32$

Where Input_bits is the number of bits that the input signal actually uses, length_bits is the number of bits required by the filter length, and order is the actual filter order (1 or 2). For example, an input having a maximum of 12 bits can be filtered with a length of 1024 (10 bits) and order 2. However, using a 16-bit input value and order 2 allows only a maximum length of 256 (8 bits). It is the user’s responsibility to ensure that this is fulfilled.

To ease further processing and transfer of values, the output can be shifted right by using the OUTSHIFT(CICCON1[4:0]) bits. When the CICxDOUT values are read from the register, they will be shifted right by the value set by OUTSHIFT. Shifting can be disabled by setting the OUTSHIFT value to zero.