Interface device for interfacing a network station to a physical network

Abstract

An interface for a connection network between individual stations and a physical medium used for the message traffic between these stations, where signals supplied via the physical medium are converted into a bit stream by means of a demodulator, such a bit stream being converted into signals to be transmitted via the physical medium by means of a modulator, a protocol control unit is connected thereto and communicates, via a communication memory bus, with a communication memory a first part of which is reserved for the communication software which is stored as the primary program. A second part of the communication memory is reserved for the process control software which is stored at least partly as the secondary program for the process to be executed in the station connected to the interface, the protocol control unit consisting of a modem control unit for writing and reading the bit stream received and to be transmitted, respectively, into and from the communication memory, a communication control unit for coordinating the operations of the modem control unit and for ensuring the execution of the primary and the secondary program, and a communication memory bus control unit for assigning time slots for access to the communication memory in response to relevant requests from the modem control unit and the communication control unit, the modem control unit interrupting the execution of the secondary program in the communication control unit each time when a communication instruction is to be executed for the relevant station, after which the communication control unit executes the primary program but continues the execution of the secondary program during waiting periods in the execution of the primary program, for which purpose there is provided a further memory for memorizing the location where and the circumstances under in the primary and the secondary program have been interrupted.