meysam_abbasinia said:they can copy external memory easy. this way is not good.
I used battery backup rtc with ram to store the serial number. when they take the chip to read it's memory, all data has been cleared.
Each Device has a Unique 64-Bit Serial Code Stored in an On-Board ROM
64-BIT LASERED ROM CODE
Each DS18B20 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits
of the ROM code contain the DS18B20’s 1-Wire family code: 28h. The next 48 bits contain a unique
serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is
calculated from the first 56 bits of the ROM code. A detailed explanation of the CRC bits is provided in
the CRC Generation section. The 64-bit ROM code and associated ROM function control logic allow the
DS18B20 to operate as a 1-Wire device using the protocol detailed in the 1-Wire Bus System section.
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