To avoid contention between master stations in the case of issuing an emergency control command directly from the master station to a slave station in an emergency.
A master station 1 periodically polls information of slave stations 2-1-n and transmits the information to a computer 3 via a system bus 4 when there is no error. When a slave station state identification processing section 16 detects an error in the slave station information, the processing section 16 decides whether or not a condition defined in a control pattern storage section 17 holds and when it holds, the processing section 16 determines priority of the error and starts a contention management section 18. The contention management section 18 compares priority of an emergency control command of other master station entered in a priority information storage section 19 with the priority of its own station and executes the emergency control command when the priority of its own station is higher. When the priority of its own station and that of the other master station are in contention, the slave station information defined in a detailed condition of a control pattern is collected and when the detailed condition is not established, the priority of its own station is decreased and the resulting priority is compared again.
TAHIRA MITSUHIRO
KAWAI YOSHINORI
KOMATSU SADANORI
SUGIMOTO MANABU
HITACHI ENG CO LTD
IBARAKI HITACHI JOHO SERVICE K