Since 2010, our recommendation is to migrate from 4-byte unique IDs to 7-byte unique IDs (UID), as 4-byte UIDs are not available anymore due to the limited number of IDs from of bytes.
Information of the limitation number of 4-byte ID was shared in 2010.
The 4-byte ID is defined by the international standard ISO/IEC14443-3. The four bytes are split into the bytes UID0 to UID4, whereby in the second half of the byte UID0 the Identifier Range is contained.
ISO allows to use the green marked Identifier ranges as shown in the graph below. The rest of the bytes are continues numbers from the database out of the specific Identifier Range.
This information should help to define the way the 4-byte HEX number is converted to the DEC number.
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