| 摘要 |
PURPOSE:To perform the priority processing for the poll request within each terminal in accordance with the degree of urgency and thus to reduce the occurrence probability of the overrun in the series loop transmission system in which the data transmission lines are formed into a loop formation. CONSTITUTION:Central station 1 and plural units of terminal 2 are connected into a series loop, and a polling is given to terminal 2 through station 1 to perform the data communication. In this system priority level PL to show the degree of urgency for the poll request of terminal 2 using the slot is provided to time slot 4, along with alteration display bit C and synchronous bit SNC. And SNC is detected through synchronous bit detecting circuit 6 at each terminal 2, and PLC conversion circuit 9 is started. Thus, whether poll request 19 of the own terminal is higher than the degree of request shown by level PL is decided. If request 19 is higher than the request degree, level PL of slot 4 is altered to the higher priority and displayed on display bit C to be then transmitted to loop 3 via loop transmission circuit 12. |
