A system for generating CRC code words associated with data ranging up to w-bytes in width. The system is an iterative approach for providing a CRC calculation circuitry with the CRC calculation being subdivided into a blocks with selectable bus widths which blocks can be cascaded to provide calculation for a parallel bus width of any arbitrary number of bytes. The circuitry includes a first plurality of serially coupled code-generation blocks each for generating a CRC value based on data input to each block; a second plurality of parallel coupled code-generation blocks each for generating a CRC value based on data inputs, and, a device for selecting particular CRC code generation blocks in the first and second pluralities to be included in a CRC calculation based on the data input such that any number of data input bytes may be processed.