topic Re: Query on Card Detection IRQ for RC522 in NFC

Query on Card Detection IRQ for RC522

Saranya20491 — Mon, 10 Nov 2025 12:42:01 GMT

Hi ,

I am working with the RC522 RFID module and have a question regarding card detection interrupts.

When i worked on SL030, there is a dedicated card detection interrupt available.

I noticed that the RC522 development board has an IRQ pin, and according to the datasheet, different interrupt sources can be routed to this pin using the ComIrqReg register (address 0x04).

However, after reviewing the available interrupt sources, I could not find one specifically for card detection. Could you please confirm if the RC522 supports a dedicated card detection IRQ, or if card presence must be detected via polling?

Thank you for your support.

Re: Query on Card Detection IRQ for RC522

Fabian_R — Mon, 10 Nov 2025 17:36:04 GMT

Hello sir,

Thank you so much for your interest in our products.

MFRC522 isn't recommended for new designs, for this reason our recommendation is to please explore the possibility of using CLRC663 plus family ICs.

Regarding the tag you are trying to read, please keep in mind that SL2 and SL3 are either ICODE or UCODE products respectively. ICODE are ISO15693 tags that, can't be read by the MFRC522 since this Reader IC is intended to only interface with NTAGs and MIFARE cards. Is possible that the MFRC isn’t actually communicating with the Tag.

The IRQ pin available is intended for the actual data exchange with the Host. As shown in Table 18. Those are the event's that can trigger the IRQ pin. If you are looking of a card detection pin, my recommendation would be to change to CLRC663, where It has a Low-power card detection feature that wakes up when the card is near the reader's antenna and the detuning of the antennas sends the IRQ to the host.

If there is any further information I could help you with please do not hesitate on letting me know.

Re: Query on Card Detection IRQ for RC522

Saranya20491 — Tue, 11 Nov 2025 05:13:18 GMT

Hello,

Thank you for your response. I would like to clarify my question regarding the MFRC522.

I understand that the IRQ pin can be triggered by events such as data transfer, timer events, and other communication-related signals, as listed in Table 18 of the datasheet.

My question is: is it possible to infer the presence of a card using any of the available IRQ sources on the MFRC522, rather than sending the ATQ command for polling?

In other words, even if there is no dedicated card detection interrupt, can any way the existing IRQ triggers be reliably used to detect when a new card is brought into the reader’s field, so that card detection can be event-driven instead of continuously polling the card?

Re: Query on Card Detection IRQ for RC522

Fabian_R — Tue, 11 Nov 2025 18:39:18 GMT

Hello sir,

Unfortunately, there isn't a built-in feature that is able to do this.

We understand this is a great feature. For this reason, it was built-in or latest NFC Frontend devices.