IC CARD

摘要

PURPOSE:To decide whether a threshold satisfies a standard value or not by comparing the threshold of a memory transistor TR with the standard value and extending the erase and write time when the threshold is smaller than the standard. CONSTITUTION:When a data write instruction is inputted to an IC card, a CPU inputs data 'FFH' to a byte selected by a Y gate 4 through a data bus 13. A control circuit 8 applies a high voltage generated by an erase and write voltage generating circuit 9 to a proper position and writes 'FFH' in the selected address. After the reference voltage from a reference voltage generating circuit 3 is given to a sense amplifier 2, written data is read out. This data is read into the CPU and is collated with 'FFH'. If this collation results in disaccord, it is decided whether the number of times of collation reaches a prescribed value or not; and when it does not reach the prescribed value, the write time is extended to write 'FFH' again.