1. In a communication control unit, useful in a data processing system having a central processing unit coupled to a main memory, and having a plurality of peripheral devices, each for communicating with said data processing system and each capable of handling messages in accordance with a different communication discipline, said communications control unit responding to messages from each peripheral device and transmitting messages to each peripheral device in accordance with the discipline defined therefor, said communication control unit comprising: a programmable controller module including: program memory means including a plurality of locations each storing an instruction, with sequences of instructions forming (1) control routines common to all peripheral devices and (2) character transmit/receive routines each unique to a particular communication discipline used by one or more of said peripheral devices; instruction register means; program address counter means for identifying a location in said program memory means and for transferring the instruction stored therein to said instruction register means; a read/write memory means for storing data; a data bus comprised of parallel bit lines; means responsive to instructions transferred to said instruction register means for operating on data either in said read/write memory means or appearing on said data bus; a direct memory access module means responsive to instructions transferred into said instruction register for transferring data from said read/write memory to said main memory and from said main memory to said read/write memory; and an interface adaptor means coupled between said programmable controller parallel data bus and said peripheral devices for receiving data from and transmitting data to said peripheral devices serial by bit.