What is the sequence of operations in which the PCD and PICC start a conversation?

* Question

What is the sequence of operations in which the PCD and PICC start a conversation?

* Answer

In contactless smart card communication—such as in NFC or RFID systems—the Proximity Coupling Device (PCD) initiates and manages communication with the Proximity Integrated Circuit Card (PICC). This communication follows a well-defined sequence governed by standards such as ISO/IEC 14443 (widely used in contactless payment and identification systems).

Sequence of Operations: PCD–PICC Communication

Field Activation (PCD →)
The PCD generates a radio frequency (RF) field, typically at 13.56 MHz, to power and detect nearby PICCs. This field serves both as a power source (for passive PICCs) and as a communication carrier.

Polling and Request (REQA or WUPA) (PCD →)
The PCD sends a Request Command (REQA) or Wake-Up Command (WUPA) to detect any PICC within range and to initiate the anti-collision process.

PICC Response (ATQA) (PICC →)
The PICC responds with an Answer to Request (ATQA), which includes information about its communication capabilities and type (Type A or B, for example).

Anti-Collision and Selection (PCD ↔ PICC)
If multiple PICCs are present, the PCD performs an anti-collision procedure to identify and select one PICC uniquely:

The PCD sends Select commands (e.g., SEL, CL1, CL2).

The PICC responds with part or all of its UID (Unique Identifier).

The PCD confirms selection by sending a Select Acknowledge (SAK) command.

Activation (PCD →)
After a PICC is selected, the PCD may send RATS (Request for Answer to Select) to initiate higher-layer protocol parameters negotiation (e.g., for ISO 14443-4 cards).

PPS (Optional, PCD →)
If needed, a Protocol and Parameter Selection (PPS) command is sent to negotiate communication speed or frame size.

Data Exchange (PCD ↔ PICC)
With the communication channel established, the PCD and PICC can now exchange application-specific data (e.g., payment information, access control credentials).

Deactivation or Halt (PCD →)
After the data exchange, the PCD may deactivate the PICC or issue a Halt command, ending the session. The PCD can then move on to another PICC if multiple cards are present.

Summary Table

Real-World Examples:

Contactless Payment (e.g., Visa payWave, Mastercard PayPass)
Follows the ISO/IEC 14443 protocol to initialize, authenticate, and perform secure transactions.

Access Control Cards
Use the same initiation sequence to identify users and grant or deny access.

Conclusion:
The PCD initiates and controls the conversation with the PICC through a carefully structured sequence of steps involving field generation, polling, anti-collision, activation, and data exchange. This structured flow ensures reliable, secure, and efficient communication, even in environments with multiple contactless cards.