ST25R3918 datasheet(40/141 Pages) STMICROELECTRONICS

40 / 141 page

Application information

ST25R3918

40/141

DS13490 Rev 2

Passive target

Communication can be performed by the host (through FIFO) or also by using automatic

responses as referred in Passive target definition register.

These automatic responses include for NFC-A the complete anti-collision including SAK.

Handling of RATS and HLTA is up to the host. For NFC-F only the SENSF_REQ is handled

by sending SENSF_RES.

States of NFC-A can be handled by observing Passive target display register and Passive

target interrupt register bits I_wu_a, I_wu_a*. Direct commands Go to sense and Go to

sleep let the host influence the passive target states.

Responses to SENSF_REQ can be observed by thanks to bit I_wu_f.

The content of the automatic responses is defined by content of PT_Memory.

Bit rate detection mode

The Listen mode can also be started from the so-called Bit rate detection mode. In this

mode the communication mode is not fixed. This mode is activated in case of Target mode

together with bit om3 set to 1.

The other om bits define the technologies to be recognized. It is an extension of the Fixed

listen communication mode.

Once the reception of the first frame starts, the Bit rate detection mode signals an IRQ I_nfct

indicating that the bit rate has been identified and the host can retrieve the related

information by reading nfc_rate on Bit rate definition register.

When the first frame has been fully received, the host can exit the Bit rate detection mode

by setting the corresponding mode on om<3:0> bits in the Mode definition register to the

corresponding fixed listen communication mode.

Bit d_ac_ap2p allows filtering of NFCIP-1 active frames.

Low power field detection

The Fixed listen communication and Bit rate detection modes can be enhanced in terms of

power consumption by using the field detector in Low-power mode, putting the ST25R3918

in power-down mode (en = 0) while waiting for an external field from a peer/reader.

For this mode the Bit rate detection mode or the Fixed listen communication mode have to

be selected, and bits en, rx_en and tx_en in the Operation control register need to be

cleared to 0.

In this mode the field detector has to be configured to automatic or manual peer detection

threshold.

On detection of external field (I_eon) the ST25R3918 temporarily enable the oscillator and

the receiver. The host needs to confirm it by setting en and rx_en option bits in the

Operation control register within 10 ms.

From this point on normal bit rate detection or normal target communication can be

performed.

PT memory

The PT_Memory is used to store data for NFCIP-1 passive target and NFC-A card/listen

mode. It is loaded via the host interface as described in Section 4.3.

ST25R3918 Datasheet(PDF) 40 Page - STMicroelectronics

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