1. In a data processing system responsive to a single stream of instructions, wherein the data processing system comprises: a general purpose processor adapted to independently decode and execute each of a first predetermined subset of said instructions; and any of a plurality of special purpose coprocessors each adapted to cooperate with the processor in the independent decoding and execution of each of a respective second predetermined subset of said instruction; the processor comprising: first means for receiving each of said instructions comprising said stream of instructions; second means for detecting in a predetermined operation bit field of each of said received instructions a predetermined bit value characteristic of each and every one of said instructions comprising said second subset of said instructions; third means for providing to said coprocessor from a predetermined command bit field of each of said detected instructions any of a plurality of predetermined command signal values each of which indicates a predetermined command which must be performed by said coprocessor in support of the execution of said detected instruction by the processor; fourth means for receiving from said coprocessor a response to the receipt of said command, said response comprising any of a plurality of response signal values each of which indicates whether a predetermined task must be performed by said processor in support of the performance of said command by said coprocessor; and fifth means for performing said task if indicated by said received response signal value.