PS081 datasheet(79/155 Pages) AMSCO

79 / 155 page

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PSØ81

the transmitted data with the EEPROM content. The result is available after 1 ms on the SDO port.

=xFF stands for correct data, 0x00 for wrong data.

An unauthorized person has to test all possible combinations. This will last for 2^64 bits * 10 ns =

5849 years just for one read.

Figure 4.16 Read protection

NOTE: E0, E2...E6 are the lower byte, E1, E3....E7 are the corresponding higher bytes in a word.

User-EEPROM Read Access

The upper 48 bytes of the EEPROM, address 2000 to 2047, are specified as userEEPROM. The

user EEPROM is also accessed word-wise (16 bits) when addressed through the SPI interface. It is

possible to read from these cells by means of opcode userEEPROM_read. userEEPROM_read reads

back one 16 bit word.

Figure 4.17 User-EEPROM read access

EEPROM Write Access

The EEPROM is split into four blocks of 512 bytes or 256 words. The blocks are addressed by the

lowest two bits of the first sent address byte. All write commands are followed by 16 bit data words

with the lower 8 bits to be sent first. Programming is started by a sixth data word and stopped 4 ms

later by a seventh data byte.

It is not possible to write a word into an EEPROM cell that is not empty. So it is not possible to fill up

a word to 0xFFFF (additional measure to protect from unauthorized reading).

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