Semiconductor disk unit with processor for diagnosis and communication with external device through a two lines bus

A data storage device comprising:

• an interface control means coupled to a host device through an interface;
• a device section comprising a memory means and a memory control means coupled to said interface control means and to said memory means;
• a control means, coupled to said interface control means and to said memory control means and also coupled to an external device or to a second host device through a pair of data transmission and reception lines, for controlling said interface control means and said memory control means, and for executing diagnosis and test of said device section by interruption processing upon reception of a control command from said external device, said control means including:
• means for determining whether said received command is correct;
• means, responsive to the received command not being correct, for reporting that the received command is not correct to said external device;
• and
• means, responsive to the received command being correct, for executing the received command by means of said interruption processing and for reporting the result of such execution to said external device through said transmission data signal line.