Patent ID: 8578065

Claim:
A communication speed control apparatus for controlling communication between a host device and an external device in accordance with a high-speed communication mode or a low-speed communication mode, the apparatus comprising: a list storage unit configured to store a list of specification information of external devices that are incompatible with the host device when data communication is carried out using the high-speed communication mode; a specification information obtainment unit configured to obtain external device specification information from the external device; a device determination unit configured to determine if the external device specification information obtained from the external device corresponds to an incompatible external device based on the stored specification information; a cable length input unit that accepts cable length information inputted by a user operation, specifying a length of a cable that connects the host computer to the external device; a cable length determination unit that determines if the cable length specified is greater than or equal to a predetermined value; a communication speed control unit configured to set a data communication speed to the low-speed communication mode if the device determination unit determines that the external device is incompatible with the host device or determines that the cable length is greater than or equal to the predetermined value, wherein setting of the low-speed communication mode is performed prior to a start of data communication between the host device and the external device; and the communication speed control unit performing a bus reset to reset the speed mode of the data communications if the external device does not correspond to an incompatible external device and if the cable length is less than the predetermined value.