ST25R3911B datasheet(69/129 Pages) STMICROELECTRONICS

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ST25R3911B

Functional overview

transparent mode is that the emission of the carrier field has to be enabled only during Tx.

This is done by writing the Operation Control Register before and after Tx. Since with every

SPI command the Transparent mode is lost it has to be re-entered.

In order to receive the reply in active NFC communication mode only the AM demodulation

channel is used. Due to this the receiver AM channel has to be enabled, while PM can be

disabled.

Implementing active communication requires detection of external field. Setting the bit en_fd

in the Auxiliary Definition Register enables the External Field Detector with Peer Detection

Threshold. When bit en_fd is selected and the ST25R3911B is in Transparent mode, the

External Field Detector output is multiplexed to pin IRQ. This enables detection of external

target/initiator field and performing RF collision avoidance.

In case timing of the NFC Field ON command is correct for the NFC active protocol being

implemented, these commands can be used in combination with the Transparent mode.

These commands are used to perform the RF collision avoidance, switching on the field and

timing out the minimum time from switching on the field to start of transmitting the message.

After getting the interrupt, the controller generates the message in the Transparent mode.

When bit en_fd is set and all bits of the Operation Control Register are set to 0 the

ST25R3911B is in the low power NFC Target Mode (same as in case of setting of targ bit,

(see NFCIP-1 Active Communication Target). In this mode initiator field is detected.

After getting an IRQ with I_eon flag set, the controller turns on the oscillator, regulator and

receiver and performs reception in the Transparent mode.

MIFARE™ Classic compatibility

For communication with MIFARE™ Classic compliant devices the bit6 and bit7 from the

ST25R3911B can be used to send and receive MIFARE™ Classic compliant or custom

frames.

Stream mode

Stream mode can be used to implement protocols, where the low level framing needed for

ISO14443 receive coding can be used and decoded information can be put in FIFO. The

main advantage of this mode over the Transparent mode is that timing is generated in the

ST25R3911B therefore the external controller does not have to operate in real time. The

stream mode is selected in the Mode Definition Register, the operating options are defined

in the Stream Mode Definition Register.

Two different modes are supported for tag to reader communication (Sub-carrier and BPSK

Stream Modes). General rule for Stream mode is that the first bit sent/received is put on the

LSB position of the FIFO byte.

After selecting the stream mode the receiver and transmitter have to be configured properly

(Analog Preset direct command doesn't apply for stream mode).

Sub-Carrier Stream Mode

This mode supports protocols where during the tag to reader communication the time

periods with sub-carrier signal are interchanged with time periods without modulation (like in

the ISO14443A 106 kbit/s mode). In this mode the sub-carrier frequency and number of

sub-carrier frequency periods in one reporting period is defined. Sub-carrier frequency in the

range from fc/64 (212 kHz) to fc/8 (1695 kHz) are supported.

ST25R3911B Datasheet(PDF) 69 Page - STMicroelectronics

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