US Patent 7126371 Multi-function IC card

When a reset signal /RESET is “L”, a flip-flop circuit holds “1”; on the other hand, a flip-flop circuit holds “0”. When the reset signal /RESET becomes “H”, the flip-flop circuits captures data in synchronous with a clock signal. When a power supply voltage returns to the initial value after an instantaneous blackout occurs, the data of the flip-flop circuits have the same value. An output signal of an exclusive-OR gate circuit becomes “L”, the output is held in a flip-flop circuit. As a result, an instantaneous blackout detection signal becomes “H”.