The Anti-Collision mechanism

The anti-collision mechanism in contactless smart card systems, including those based on ISO/IEC 14443 standards like Type A and Type B, is a crucial feature that allows multiple cards to be in the field of the reader simultaneously without interfering with each other. This mechanism ensures efficient communication in environments where there are potentially many cards present within the reader's range.

Here's how the anti-collision mechanism typically works:

1. Initialization

When a contactless smart card enters the electromagnetic field generated by the reader, it undergoes an initialization process. During this process, the card sends its unique identifier (UID) or serial number to the reader.

2. Anti-Collision Protocol

 The anti-collision protocol is then employed by the reader to manage multiple cards within its field. There are different anti-collision protocols specified for different standards. For example, ISO/IEC 14443 Type A and Type B standards each have their own anti-collision protocols.

3. Identification

 Using the anti-collision protocol, the reader can identify multiple cards present in its field by their unique identifiers. The anti-collision protocol ensures that each card is addressed individually and that communication with each card is not disrupted by the presence of other cards.

4. Collision Resolution

 In case of a collision, where multiple cards transmit their identifiers simultaneously and their signals overlap, the anti-collision protocol facilitates collision resolution. This may involve techniques such as time-slot allocation or binary tree algorithms to identify and select one card at a time for further communication.

5. Selection

 Once collisions are resolved and individual cards are identified, the reader can select a specific card for further communication based on criteria such as priority or specific commands from the application.

6. Communication

With the anti-collision process completed and a card selected, the reader can proceed with data exchange and transactions with the chosen card.

Overall, the anti-collision mechanism is essential for ensuring reliable and efficient communication between contactless smart cards and readers, especially in scenarios where there are multiple cards present within the reader's field. It helps prevent communication conflicts and ensures that each card is addressed and processed correctly by the reader.

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