FM4428 Secure Memory Card with 1024 x 8 Bit EEPROM

The FM4428 is a standard, low-cost EEPROM memory smart card with 1Kbyte storage space. It is a protected smart card that consists of 1,024 bytes of EEPROM memory. After eight successive incorrect entries the error counter will block any subsequent attempt at PSC verification and hence any possibility to write and erase. It is no doubt that gives a sense of secure for the users. The FM4428 is a compatible replacement of the Infineon SLE4428 which was replaced with SLE5528. SLE5528 is 100% functional compatible to FM4428.

The FM4428 consists of 1024 x 8 bit EEPROM main memory and a 32-bit protection memory with PROM functionality. The main memory is erased and written byte by byte. When erased, all 8 bits of a data byte are set to logical one. When written, the information in the individual EEPROM cells is, according to the input data, altered bit by bit to logical zeros (logical AND between the old and the new data in the EEPROM). Normally a data change consists of an erase and write procedure. It depends on the contents of the data byte in the main memory and the new data byte whether the EEPROM is really erased and/or written. If none of the 8 bits in the addressed byte requires a zero-to-one transition the erase access will be suppressed. Vice versa the write access will be suppressed if no one-to-zero transition is necessary. The write and the erase operation takes at least 2.5 ms each.

Each of the first 32 bytes can be irreversibly protected against data change by writing the corresponding bit in the protection memory. Each data byte in this address range is assigned to one bit of the protection memory and has the same address as the data byte in the main memory which it is assigned to. Once written the protection bit cannot be erased (PROM).

The FM4428 provides a security code logic which controls the write/erase access to the memory. For this purpose the FM4428 contains a 4-byte security memory with an Error Counter EC (bit 0 to bit 2) and 3 bytes reference data. These 3 bytes as a whole are called Programmable Security Code (PSC). After power on the whole memory, except for the reference data, can only be read. Only after a successful comparison of verification data with the internal reference data the memory has the identical access functionality of the FM4428 until the power is switched off. After three successive unsuccessful comparisons the Error Counter blocks any subsequent attempt, and hence any possibility to write and erase.