SLE4428 Secure Memory Card is one of the most popular “Smart Memory Cards” in the world. This chip includes an intelligent 256-Byte EEPROM with Write Protect Function and Programmable Security Code (PSC). The chip contains an EEPROM organized 1024 x 8 bit offering the possibility of programmable write protection for each byte. Reading of the whole memory is always possible. The memory can be written and erased byte by byte. Input data and the contents of the adressed byte are compared so that only bits are written which were not written before. Erasing is only possible byte-wise, even if only one bit is to be erased, but bits may be written individually. Each byte can be write/eraseprotected individually by setting a protect bit (EEPROM → ROM). The protect bit is only one time programmable and cannot be erased.