Method and apparatus for signal interfacing capable of infallibly notifying a status of an apparatus

An interface apparatus which connects between a host system and a data processing device and includes a parallel interface function for transmitting data, command, and status signals which are communicated therebetween, comprising:

• energy saving mode control means for selectively switching the apparatus to an energy saving mode from an idling mode in response to a predefined event and, in said energy saving mode, cutting off power for driving an interface circuit, except for a minimal power required to be supplied to at least one predefined portion of the interface circuit;
• and
• interface circuit control means for notifying said host system of statuses of said interface apparatus using at least one of said status signals and, after having entered said energy saving mode, maintaining said at least one status signal at a logic level which is reversed from a usual logic level thereof in said idling mode.

A data processing apparatus which connects to a host system and includes a parallel interface function for transmitting data, command, and status signals which are communicated with s aid host system, comprising:

• an energy saving mode controller which selectively switches the apparatus to an energy saving mode from an idling mode in response to a predefined condition and, in said energy saving mode, cuts off power for driving an interface circuit, except for a minimal power required to be supplied to at least one predefined portion of the interface circuit;
• and
• an interface circuit controller which notifies said host system of statuses of said interface apparatus using at least one of said status signal and, after having entered said energy saving mode, and maintains said at least one status signal at a logic level which is reversed from a usual logic level thereof in said idling mode.