IC card compatible with different supply voltages, IC card system comprising the same, and IC for the IC card

An IC card compatible with different supply voltages applied by external units, comprising:

• a peripheral circuit having a memory for storing data;
• a central processing unit (CPU) for controlling the operation of the peripheral circuit;
• means for detecting the plurality of supply voltages;
• means for testing whether the detected supply voltage applied from one of the external units is within one of a plurality of normal voltage ranges for the IC card or within abnormal voltage ranges;
• and
• means for changing a clock frequency so as to adjust a given circuit incorporated in the IC card, only when a result of the supply voltage test indicates a predetermined normal voltage range;
• wherein the plurality of normal voltage ranges comprises higher and lower voltage ranges, and the clock frequency changing means decreases the clock frequency only when the result of the supply voltage test indicates the lower voltage range.

An IC card system having an IC card compatible with different supply voltages, and external units for applying the different supply voltages and sending a clock signal to the IC card, wherein,

• (a) the IC card comprising:
• a peripheral circuit having a memory for storing data;
• a central processing unit (CPU) for controlling the operation of the peripheral circuit, the CPU comprising:
• means for testing whether the detected supply voltage applied from one of the external units is within one of a plurality of normal voltage ranges for the IC card or within abnormal voltage ranges;
• and
• means for adjusting a given circuit incorporated in the IC card, only when a result of the supply voltage test indicates a predetermined normal voltage range, and
• means for detecting the plurality of supply voltages;
• and
• (b) the external units, each comprising abnormality handling means for disabling communication between the IC card and one of the external units or ejecting the IC card if the detected supply voltage is abnormal;
• wherein the plurality of normal voltage ranges comprises higher and lower voltage ranges, and the clock frequency changing means decreases the clock frequency only when the result of the supply voltage test indicates the lower voltage range.

An IC card system having an IC card compatible with different supply voltages, and external units for applying the different supply voltages and sending a clock signal to the IC card, wherein,

• (a) the IC card comprising:
• a peripheral circuit having a memory for storing data;
• a central processing unit (CPU) for controlling the operation of the peripheral circuit, the CPU comprising:
• means for testing whether the detected supply voltage applied from one of the external units is within one of a plurality of normal voltage ranges for the IC card or within abnormal voltage ranges;
• and
• means for adjusting a given circuit incorporated in the IC card, only when a result of the supply voltage test indicates a predetermined normal voltage range, and
• means for detecting the plurality of supply voltages;
• and
• (b) the external units comprising a first external unit supplying a first supply voltage and a second external unit supplying a second supply voltage lower than the first supply voltage, and the clock frequency changing means decreases the clock frequency only when the result of the supply voltage test indicates the second supply voltage lying in the predetermined normal voltage range, each of the external units comprising abnormality handling means for disabling communication between the IC card and one of the external units or ejecting the IC card if the detected supply voltage is abnormal.