Information processing systems having a main CPU and a sub-CPU which controls the overall system to achieve power savings

An information processing system comprising:

• a main CPU having an operation mode in which the main CPU consumes a first amount of power for performing first predetermined processing and a halt mode in which the main CPU consumes a second amount of power which is less than said first amount of power;
• a plurality of input/output units including a keyboard, a timer and a display unit;
• a sub-CPU, operatively connected to said main CPU and said plurality of input/output units, for performing second predetermined processing including key input monitoring of said keyboard, timer output counting of said timer and power supply monitoring of a power supply;
• a memory unit connected to said main CPU and storing programs and data;
• and
• a power supply control circuit, connected to said main CPU, said sub-CPU and said plurality of input/output units, for controlling power supply to said plurality of input/output units and said main CPU in response to commands from said sub-CPU, wherein:
• said sub-CPU comprises means for placing said main CPU in said halt mode while said sub-CPU is awaiting a key input of said keyboard during said key input monitoring and circuitry for controlling said power supply control circuit to cease power supply to each one of said plurality of input/output units that is not currently in use while said sub-CPU is performing said key input monitoring,
• said power supply control circuit comprises means for causing initial activation of said sub-CPU in response to turn on of a main power supply, and
• said sub-CPU further comprises means, responsive to said initial activation, for causing subsequent activation of said main CPU and means, responsive to an OFF-indicating condition of the main power supply, for causing said main CPU to perform termination processing including register saving in said memory unit and, when said termination processing is completed, for controlling said power supply control circuit to turn off power supply to said main CPU and said plurality of input/output units and then to turn off power supply from the main power supply, wherein said main CPU includes means for performing, after said subsequent activation, a resume ON check to determine whether said main CPU is to continue a previous processing, and if so, for restoring previous data stored in said memory unit and then resuming said previous processing wherein:
• said plurality of input/output units further comprise a modem, a floppy disk drive and an extension slot, and
• said sub-CPU comprises means for controlling said power supply circuit, in response to receipt from said main CPU of turn on and turn off requests that relate individually to said display unit, said modem, said floppy disk drive and said extension slot and that are associated with input commands and data processing executed by said main CPU, to cause individual turn on and turn off of said display unit, said modem, said floppy disk drive and said extension slot during execution of said input commands and said data processing by said main CPU.