A plurality of memory devices of mixed type (e.g., DRAMs, SRAMs, MRAMs and NAND-, NOR- and AND-type Flash memories) are serially interconnected. Each device has device type information on its device type. A specific device type (DT) and a device identifier (ID) contained in a serial input (SI) are fed to one device of the serial interconnection. The device determines whether the fed DT matches the DT of the device. In a case of match, a calculator included in the device performs calculation to generate an ID for another device and the fed ID is latched in a register of the device. The generated ID is transferred to another device of the serial interconnection. In a case of no match, the ID generation is skipped and no ID is generated for another device. Such a device type match determination and ID generation or skip are performed in all devices of the serial interconnection. In cases of different device types being separately provided to the interconnected devices, sequential IDs are generated in each of the different device types and also the total number of each device type are recognized. In a case of a “don't care” code is provided to the interconnected devices, sequential IDs are generated and also, the total number of the interconnected devices is recognized, regardless of the type differences.