INTERFACE BETWEEN BUS AND CONNECTING METHOD OF BUS

PURPOSE: To maintain data coherence between master and a slave. CONSTITUTION: A connected first bus M connects several self-identification masters M1 and M2, and a second bus S connects the several master devices with several slave devices S1-SN, and the connected devices are not provided with a mechanism which identify themselves. A pair of registers for each slave device connected through the second bus S are integrated in an interface 10. One register 25 stores a busy tone bit when the corresponding slave is being used for the master. A second register 30 stores the identification code of the master which charges the corresponding slave with a task. When the salve accepts the task for the master, and commands the master to give up the bus, the busy tone register 25 is set, and the master identification register 30 stores the identification code of the charging master. Afterwards, when the master identification code is not belonging to the charging master, the master is not allowed to perform access to the slave which is being used.