RFID - Elektor

8 Cards and Tags in Application
8.1 ISO/IEC 14443 Type A Card Activation
The card activation sequence is identical for all MIFARE family and ISO/IEC 14443 Type
A-compatible products, so it can be universally implemented in software. Reader software
should take the following requirements into consideration:
• there may be several cards in the reader field at one time;
• card activation should work regardless of card application;
• the number of bytes in the card’s serial number (UID) is product-dependent.
After activation, it must be determined whether or not the card supports the ISO/IEC
14443 Part 4 standard T=CL transmission protocol.
In practice, an increasing number of reader systems are being designed that don’t meet
the first two requirements. This is due to the fact that the anti-collision is only possible
with proper hardware support (reader IC). Systems with reader ICs either partially or
completely omit the implementation of the anti-collision algorithm. In principle, these
systems work, but they can’t be extended later on. For example, sometimes only cards
with 4-byte UIDs are supported, meaning that 7-byte UID cards can’t be activated. Another
common mistake is the strict evaluation of card responses during activation. Readers
that only accept cards with specific ATQA and SAK values are not uncommon. In
these cases, problems only arise when these systems need to be expanded. For installations
with a large number of readers, a firmware update is only possible at high cost
and then often with great logistical complexity.
8.1.1 Card Types from the Perspective of Card Activation
Smart Card Magic.NET’s toolbar offers a very simple way to activate a card. After opening
the USB port (Open button), you need only click the Activate button to activate the
card currently in the reader’s field.
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Considering only card activation, we have the following distinguishing features:
• Length of the card serial number (4 bytes, 7 bytes and 10 bytes)
• UID (Unique ID) or RID (Random ID)
• Standardized (T=CL) and/or proprietary transmission protocol (MIFARE)
Figure 8.1 shows all possible card activation possibilities currently available. A larger
number of bytes in the UID means that the activation time increases slightly due to an
additional command sequence. Therefore, no cards with 10-byte UIDs are manufactured.
The reader software (firmware) should be prepared for future card types and should
therefore support all three UID lengths defined in the ISO/IEC 14443 standard.
The observant reader will have noticed that, in Figure 8.1, (Cards 4 and 5), 8 UID bytes
are shown. The additional byte always has the same value (0x88) and indicates that
there are twice as many UID bytes. Of these 8 bytes, only 7 are unique). So, although
we speak of a 7-byte UID (double size), a total of 8 bytes is transferred between card
and reader. This additional byte, known as the Cascade Tag (CT) in the ISO/IEC 14443
standard, should not be used by the reader software to detect a double- or triple-size
UID, however.
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