Data communications system and data communications method between distributed controllers connected by serial bus

A data communications system in which a plurality of processing devices comprising a serial bus interface, a storage unit to store data, and a processing unit to output an access request to said storage unit are connected to each other via a serial bus, wherein:

• a communication control line which connects in daisy chain between said processing devices and performs the transfer of transmission right which permits data transmission to the serial bus is provided, and
• at least one processing device of said processing devices includes a transmission right management unit which performs the transfer of the transmission right between other processing devices connected via said communication control line and manages a state of the transmission right within said processing device,
• an interface unit which when a write access request is made from said processing unit to said storage unit, writes data to said storage unit and generates a data transmission request to which an address of write destination and data are added, and when a read access request is made from said processing unit to said storage unit, reads out corresponding data from said storage unit and passes the same to said processing unit,
• a data transmission unit which receives said data transmission request and when the transmission right of said processing device is valid starts data transmission to the serial bus, and when the transmission right is invalid holds data transmission until the transmission right becomes valid,
• a data receiving unit which receives data transmitted from other processing devices connected to the serial bus and stores the same in said storage unit, and
• a state initialization unit which sets an initial state of said processing device so that only the transmission right of one processing device is valid among the plurality of processing devices connected to the serial bus at the initialization.