Patent ID: 6952404

Claim:
In a communication system wherein a master station and a slave station are connected using two redundant buses and communication between said master station and said slave station is selectively controlled; a processor for controlling said master station as a whole; a first communication means for simultaneously sending out command frames having same content from said master station to both said two redundant buses, wherein said first communication means adds check bits to said command frames; and first procedure control means for performing a test of valid data transfer using said check bits on contents of two command frames received by said slave station through said two redundant buses, for verifying conformity between contents of said two command frames, and then, depending on results of verification, for selecting a process from among the following processes: a process wherein, if command frames judged to be normal by means of said check bits are received through both redundant buses and contents of received two command frames match, said first procedure control means upon instruction by a command returns, normal end responses having same content to both redundant buses; a process wherein, if a command frame judged to be normal by means of said check bits is received through either said redundant bus, said first procedure control means upon instruction by a command returns a normal end response to only a redundant bus that received a command frames; a process wherein, if command frames judged to be normal by means of said check bits are received through both redundant buses but contents of received two command frames do not match, said first procedure control means ignores commands and returns abnormal end responses having same content to both redundant buses; and a process wherein, if a command frame judged to be normal by means for said check bits is not received through either of the redundant buses, said first procedure control means does not return any response to either of said two redundant buses.