Abstract: A communication controller for a distributed processing system has a number of data processing stations in which messages are exchanged among the stations over a communication channel. The controller includes a communications processing unit which manages the transmission and receipt of messages. A program is provided for the communications processing unit which responds to an inbound message addressed to the associated station with its poll flag asserted to cause the station to immediately contend for use of the channel. No other station can contend for use of the channel at this time because their corresponding communication processing units responded to such inbound message as being addressed to another station. This causes a predetermined time interval to start. Each of the other units then awaits expiration of the interval before attempting to contend for use of the channel.

Abstract: Interface unit for handling translation of message signals between a communication channel and a communications processor. The processor and interface unit are embodied in a data processing station of which a plurality of such stations are arranged along the communication channel. The interface unit includes a microstate machine which under program control directs the operations of message transmission, message receipt, and communication channel contention.