4-byte UIDs vs 7-byte UIDs

Forum / MIFARE general topics and applications / 4-byte UIDs vs 7-byte UIDs

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  • 15. June 2016 at 15:47
    I have a card reader that always report 64-bits, and can read cards with 4 or 7 byte uids.

    As an example, I see it can report:

    04-18-c5-82-00-00-00-00 // a 4-byte UID: uid0-uid1-uid2-uid3-00-00-00-00

    04-18-c5-82-f1-3b-81-00 // a 7-byte UID: uid0-uid1-uid2-uid3-uid4-uid5-uid6-00

    What prevents a 7-byte uid from having uid4, uid5 and uid6 from being zero? Is this covered in a spec? If so, which spec?

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    Re: 4-byte UIDs vs 7-byte UIDs

    15. June 2016 at 17:55
    In the case of 7 bytes of UID, the same are unique, so it would not be possible to find those you mention bytes 0x00 values.
    Moreover, you can find in a public document NXP (MIFARE and handling of UIDs), answer to your query.

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