ST25R3910 datasheet(25/65 Pages) STMICROELECTRONICS

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ST25R3910

Functional overview

NFC transmit commands

The NFC transmit commands (NFC transmit with Initial RF Collision Avoidance, NFC

transmit with Response RF Collision Avoidance, NFC transmit with Response RF Collision

Avoidance with n=0) are used to transmit requests and responses in the NFC mode. Before

actual transmission the RF Collision avoidance with Collision avoidance threshold defined in

the NFCIP Field Detection Threshold Register is performed.

In the command NFC transmit with Response RF Collision Avoidance n is randomly set in a

range from 0 to 3, while in the command NFC transmit with Response RF Collision

Avoidance with n=0 it is set to 0. In case collision is detected during the RF Collision

Avoidance the transmission is not done and an interrupt is sent with flag INTR due to NFC

event.

The NFC transmit commands switch on and off the transmission block, setting the

Operation Control Register bit tx_en in the NFC mode is not allowed.

Timing of the NFC transmit commands (see Table 5) is according to the ISO/IEC 18092

standard, which specifies a range for some of them.

An interrupt due to end of transmission is sent when RF field is switched off.

All NFC Transmit commands are only authorized in case the ISO mode configuration bit nfc

is set and the oscillator and regulators are running.

Mask Receive Data and Unmask Receive Data

After the direct command Mask Receive Data the signal rx_on that enables the RSSI and

AGC operation of the receiver (see Section 1.1.2: Receiver) is forced to low, processing of

the receiver output by the receive data framing block is disabled. This command is useful to

mask receiver and receive framing from processing the data when there is actually no input

and only a noise would be processed..

The direct command Unmask Receive Data is enabling normal processing of the received

data (signal rx_on is set high to enable the RSSI and AGC operation), the receive data

framing block is enabled. A common use of this command is to enable again the receiver

operation after it was masked by the command Mask Receive Data.

The command Unmask Receive Data has to be used in the NFC target mode. The

sequence implemented in the ST25R3910 supposes that every action is started with a

transmit command, after sending the transmit data, the receive mode is automatically

entered to process the response. Such a sequence is always in place in case of the

Table 5. NFC P2P timings implemented in ST25R3910

Symbol

Parameter

Value

Unit

Comments

TIDT

Initial delay time

302

μs

Initial RF Collision Avoidance

TRWF

RF waiting time

37.76

TIRFG

Initial guard time

5.11

Initial RF Collision Avoidance

TADT

Active delay time

151

μs

Response RF Collision Avoidance

TARFG

Active guard time

TGAS

Guard time after sending

response or request

Time during which RF field stays switched on

after sending a response or a request. Not

specified in the ISO/IEC 18092.

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