A programmable serial interface is disclosed for use in a semiconductor circuit that supports a plurality of communication protocols. The programmable serial interface includes one or more shared hardware components that implement tasks and functions of a plurality of communication protocols, optional protocol specific hardware, a processor and memory. For each task or function required by a supported communication protocol, a determination is made as to which parts of the function will be implemented using shared hardware, protocol specific hardware or in software. The communication protocols to be supported are identified, and the functions performed in accordance with each of the supported protocols are analyzed to identify those functions suitable for common or shared hardware with other communication protocols. In addition, unique or time-critical functions are identified that must be implemented in hardware. Finally, any functions that are not implemented in hardware are implemented in software.