External connection device, host device and data communication system

A host device connectable to an external connection device that includes a parameter register, a command register, and a controller operable, said host device comprising:

• transmission means for transmitting, to the external connection device, a parameter and an operation control command for performing operation control of said connection device,
• the parameter register of the external connection device storing the parameter, the command register of the external connection device storing the operation control command provided by said host device, and the controller of the external connection device referring to the operation control command stored in the command register and performing operation control specified by the operation control command;
• said transmission means issuing a transfer protocol command (TPC) to said external connection device to access the parameter register and the command register of the external connection device, wherein a command set of the TPC includes:
• a first register write command for requesting transmission of an arbitrary parameter from said host device to the external connection device and storage of the transmitted parameter into the parameter register of the external connection device,
• a second register write command for requesting transmission of an arbitrary operation control command from said host device to the external connection device and storage of the transmitted operation control command into the command register of the external connection device, and
• a third register write command for requesting transmission of an arbitrary operation control command and an arbitrary parameter from said host device to the external connection device, storage of the transmitted operation control command into the command register of the external connection device, and storage of the transmitted parameter into the parameter register of the external connection device.

A data communication system, comprising:

• a host device;
• and
• an external connection device connectable to said host device;
• said host device including:
• transmission means for transmitting, to the external connection device, a parameter and an operation control command indicating a command for performing operation control of the external connection device;
• said external connection device including:
• a parameter register operable to store the parameter,
• a command register operable to store the operation control command provided from the host device, and
• a controller operable to refer to the operation control command stored in the command register and to perform operation control specified by the operation control command;
• said parameter register and said command register of said external connection device being accessed from said host device based on a transfer protocol command (TPC) issued from said host device;
• a command set of the TPC including a first register write command for requesting transmission of an arbitrary parameter from the host device to the external connection device and storage of the transmitted parameter into the parameter register, a second register write command for requesting transmission of an arbitrary operation control command from the host device to the external connection device and storage of the transmitted operation control command into the command register, and a third register write command for requesting transmission of an arbitrary operation control command and an arbitrary parameter from the host device to the external connection device, storage of the transmitted operation control command into the command register, and storage of the transmitted parameter into the parameter register.