Abstract

A communication control unit useful for operably coupling a plurality of peripheral devices to a data processing system including a central processing unit (CPU) and a main system memory. The communication control unit is comprised of three major sections: (1) A direct memory access module (DMA) for communicating with the memory of the CPU; (2) A serial interface adaptor module (SIA) for converting parallel data to serial data for transmission to a peripheral device and serial data to parallel data on receiving from a peripheral device; and (3) A programmable controller module (PCM) connected between the DMA and SIA for providing the overall control of message reception and transmission. The PCM comprises a small special-purpose programmable parallel computer. A program (firmware) stored in a read-only memory of the PCM enables the PCM to handle the different communication disciplines observed by various peripheral devices operable with the communication control unit. The program may be considered as containing two levels of instructions. The first level consists of a control program containing common routines and control programs that are used by the various communication disciplines. The second level of firmware contains all communication discipline dependent instructions associated with the processing of transmit or receive characters according to the particular discipline. Just as the first level programs are used by all the communication disciplines, the application dependent programs in the second level are used by all channels on the PCM I/O bus that communicate according to the discipline represented by the instructions of these programs.