ISO 14443 Deep Dive

ISO 14443 Deep Dive

ISO 14443 is the international standard for contactless smart card communication at 13.56 MHz. It defines the physical layer, the initialisation and anticollision sequences, and the transmission protocol used by transit cards, passports, banking cards, and access badges worldwide.

Use the ATR Parser to decode the ATS (Answer To Select) returned by ISO 14443ISO 14443StandardStandard for contactless smart cards.Click to view →-4 cards, and the Card Type Identifier to distinguish card families from UID and ATS data.

Type A vs Type B Physical Layer

ISO 14443 Part 2 defines two physical layer variants operating at 13.56 MHz carrier with a base bit rate of 106 kbps. Parts 3 and 4 layer initialisation and protocol on top.

Both types support higher bit rates of 212, 424, and 848 kbps through the PCD (proximity coupling device, i.e., reader) sending a rate selection command after successful activation.

Anticollision and Card Activation

When multiple cards are within reader range, the reader must resolve which card to communicate with. The process differs by type:

Type A uses a bit-oriented loop: the reader sends a SELECT command with a known UID prefix; cards whose UID matches respond with the next bit. Collisions are resolved bit by bit, isolating one card per loop cycle.

Type B uses a probabilistic time-slot scheme: the reader broadcasts a REQB with a number-of-slots field (1, 2, 4, 8, or 16). Each card picks a random slot and responds with its ATQB if not already in HALT state. A successful ATTRIB command then dedicates the channel to one card.

After selection, both types optionally enter the ISO 14443-4 protocol layer (T=CL — contactless transport). Cards that support only Part 3 (MIFARE Classic, NTAG) terminate at anticollision and use proprietary commands. Cards that respond to RATS (Request for Answer To Select) with an ATS response support the full ISO 14443-4 command transport.

APDU over Contactless

ISO 14443-4 wraps APDUAPDUProtocolCommunication unit between card and reader.Click to view → messages in I-blocks (information blocks) with sequence numbers, R-blocks (receive-ready/not-ready), and S-blocks (supervisory: WTX, DESELECT, PARAMETERS). This block structure provides the same error-recovery semantics as ISO 7816ISO 7816StandardPrimary standard for contact smart cards.Click to view → T=1T=1ProtocolBlock-oriented smart card protocol.Click to view → over the contactless channel.

The APDU payload itself is identical to contact-mode APDUs as defined in ISO 7816-4. The SELECT AIDAIDProtocolUnique identifier for card applications.Click to view → command uses the same AID format, and responses carry the same SW1 SW2 status words. This design means a dual-interface card can expose the same applet logic to both contact and contactless readers.

NFC and ISO 14443

The NFC Forum's NFC-A (ISO 14443-3 Type A) and NFC-B (ISO 14443-3 Type B) modes map directly onto the underlying standard. A smartphone acting as an NFC reader follows the same anticollision and activation procedure as a dedicated smart card terminal, making smartphone-based card emulation (HCE — Host Card Emulation) or embedded secure element transactions possible with the same card-side APDU logic.

Key Metrics for Reader Design

Antenna design is critical: coil geometry, tuning capacitance, and quality factor Q determine both maximum range and susceptibility to detuning by nearby metal surfaces.

Continue to EMV Payment Architecture for how EMVEMVApplicationGlobal chip payment card standard.Click to view → builds a payment transaction layer on top of ISO 14443 and ISO 7816.