Priority based access control arrangement

Claim 1

Access control apparatus to control access to a communication channel of a plurality of interconnected units each one of which has an own unit priority assigned to it and includes: a receiving means to receive from a preceding unit an access request word comprising a plurality of successive request channels to which channel priorities are assigned; a writing means for writing an access request in the request channel whose channel priority corresponds to its own unit priority 1 and for transmitting the access request word to a following unit; an inhibiting means for inhibiting access of preceding units to said communication channel, wherein said channel priorities are assigned to said request channels in such a way that they are received in decreasing order by said one unit, and wherein said one unit further includes word processing means for operating said inhibiting means when during the processing of said received access request word it is detected that said own priority is not lesser than any unit priority already written in said received access request word; and detection means to detect, a predetermined interval after transmission of said access request word by a last one of said units, whether a following unit has operated its inhibiting means, in which case said one unit may not access said communication channel.