Communication system and communication control method

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 frame;
• 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 of 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.

A communication control method 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 controlled;

• wherein command frames having same content are simultaneously sent out from said master station to both of said redundant buses, check bits are added to said command frames, said command frames sent through said two redundant buses are received by said slave station, a test of valid data transfer is performed using said check bits to verify whether contents of received two command frames match, and depending on results of verification, a process is selected from among the following plurality of 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 method acts as instructed by command and returns normal end responses having same content to both said redundant buses;
• a process wherein, if a command frame judged to be normal by means of said check bits is received through either redundant bus, said method acts as instructed by command and returns a normal end response to only a redundant bus that received a command frame;
• 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 method ignores commands and returns abnormal end responses having same content to both said redundant buses;
• and
• a process wherein, if a command frame judged to be normal by means of said check bits is not received through either of said redundant buses, said method does not return any response to either of said redundant buses.

A communication system, wherein a transmitter circuit and a receiver circuit are connected to a transmission line and data is transferred between said transmitter circuit and said receiver circuit, said transmitter circuit comprising:

• transmitter means for transmitting data;
• and
• multi-strobe generation means for generating N strobe signals, wherein N is an integer, each of which has a different timing;
• and said receiver circuit comprising:
• a plurality of latch circuits equal in number to the number of N strobe signals and for successively retaining data sent by said transmitter circuit at each point in time of said N strobe signals;
• and
• sampling means for sampling data retained by said plurality of latch circuits using a receiver clock having a frequency equivalent to data transmission rate to synchronize data with said receiver clock.

A communication system, wherein bus arbitration is carried out to permit a bus master, which is incorporated in a bus master connected to a data bus and an arbitration bus and acquires right to use said data bus and after having carried out an arbitration procedure using said arbitration bus, to use said data bus, said system comprising:

• a monitor for monitoring signals on said arbitration bus;
• and
• an arbiter which upon request to use said data bus issued from a corresponding bus master executes a process from among the processes listed hereafter depending on results of monitoring:
• a process wherein, if no arbiration is carried out on said arbitration bus after said arbiter's corresponding bus master has finished using said data bus, said arbiter acquires right to use said data bus without executing an arbitration procedure using said arbitration bus;
• and
• a process wherein, if arbitration is carried out on said arbitration bus after said arbiter's corresponding bus master has finished using said data bus, said arbiter acquires right to use said data bus after executing said arbitration procedure using said arbitration bus.