Knowledge base 121 - HID Prox + MIFARE combination cards work on the door reader but not for cashless vending
Problem: My HID Prox + MIFARE combination card works on the door reader but not the cashless vending
Solution: NXP (Philips electronics) who make MIFARE chips have run out of unique identifying numbers (UID / CSN). These numbers were 32 bits (4 bytes).
To keep the UID / CSN unique NXP moved to a longer UID / CSN which is 56 bits long (7 bytes).
Some systems do not read 7 byte UID cards correctly so the cards that have been supplied may be 7 byte UID cards that are configured to report a 4 byte UID.
After conversion from a 7 byte UID to a 4 byte UID the ATQA remains the same. This still identifies the card as a 7 byte UID card although this is really only for guidance.
When the UID of the card is read using anticollision cascade level one (and not based on the ATQA) the card will be read correctly.
Many reader manufacturers have a firmware/software fix for this.
Please follow the link below page 9 footnotes 5 and 6 which shows the ATQA remaining the same once a 7 byte UID MIFARE card has been converted to report only a 4 byte UID.