Data highway access control system

摘要

An arrangement for permitting communication among a plurality of stations on a single serial data communications bus. Each station is provided a choice between two modes of operation. All stations ordinarily operate in a normal mode, seeking access to the serial bus upon occurrence of a democratic time window. In the normal mode, each station is given an opportunity to issue a single transmission before any one station is permitted to issue a second transmission. Should any station require transmission of an urgent message, that station may seek access during an autocratic time window. Within any single round of bus arbitration, all autocratic time windows occur prior to the first democratic time window.