ST25R3911B datasheet(44/116 Pages) STMICROELECTRONICS

44 / 116 page

After selecting the NFCIP-1 active communication mode the receiver and transmitter have to be configured

properly. This configuration can be done automatically by sending direct command Analog Preset (see Analog

preset).

During NFCIP-1 active communication the RF Collision Avoidance and switching on the field is performed using

NFC Field ON commands (see NFC field ON commands), while the sending of message is performed using

Transmit commands as in the case of reader communication. Alternatively the Response RF Collision Avoidance

sequence is started automatically when the switching off of target field is detected in case the bit nfc_ar in the

Mode definition register.

When NFCIP-1 mode is activated the External Field Detector is automatically enabled by setting bit en_fd in the

Auxiliary display register. The Peer Detection Threshold is used to detect target field. During execution of ‘NFC

Field ON’ commands, the Collision Avoidance Threshold is used.

Initial set-up of the Operation control register before the start of communication is the same as in case of reader

to tag communication with the exception that the transmitter is not enabled by setting the tx_en bit. The tx_en bit

and therefore switching on of the transmitter is controlled by NFC Field ON commands. Switching off the field is

performed automatically after a message has been sent. The General purpose and no-response timer control

In order to receive the NFCIP-1 active reply only the AM demodulation channel is used. Due to this the receiver

AM channel has to be enabled. The preset done by Analog Preset command enables only the AM demodulation

channel, while PM channel is disabled to save current.

In NFCIP-1 active communication the NFCIP-1Transport Frame format (see Figure 24) is always used. Due to

this the ISO14443A and NFC 106kb/s settings register bit nfc_f0 is set by Analog Preset command (see Support

of NFCIP-1 transport frame format).

NFCIP-1 active communication sequence when bit nfc_ar in the Mode definition register is set (automatic

Response RF Collision Avoidance sequence). During this sequence bits nfc_n1 and nfc_n0 of the Auxiliary

definition register have to be 0 to produce Response Collision Avoidance sequence with n=0:

The direct command NFC Initial Field ON is sent. In case no collision was detected during RF Collision

Avoidance the field is switched on and an IRQ with I_cat flag set is sent to controller after TIRFG.

The message, prepared as in case of reader to tag communication, is transmitted using Transmit command.

After the message is sent the field is switched off. The time between the end of the message and switching

off the field is defined by the General Purpose timer (the General Purpose timer IRQ may be masked since

controller does not need this information).

After switching off its field the ST25R3911B starts the No-Response timer and observes the External Field

Detector output to detect the switching on of the target field. In case the target field is not detected before

No-Response timer timeout, an IRQ due No-Response timer expire is sent.

When Target field is detected an IRQ with I_eon flag set is sent to controller and Mask Receive timer is

started. After the Mask Receive Timer expires the receiver output starts to be observed to detect start of the

target response. The reception process goes on as in case of reader to tag communication.

When the External Field Detector detects that the target has switched off its field, it sends an IRQ with I_eof

flag set to the controller, and in case bit nfc_ar is set automatically activates the sequence of direct

command NFC Response Field ON. In case no collision is detected during RF Collision Avoidance the field

is switched on and an IRQ with I_cat flag set is sent to controller after TARFG.

Sequence loops through point 2. In case the last initiator command is sent in next sequence (DLS_REQ in

case of NFCIP-1 protocol) the bit nfc_ar in the Mode definition register has to be put to 0 to avoid switching

on the initiator field after the target has switched of its field.

NFCIP-1 active communication target

The ST25R3911B target mode is activated by setting bit targ in the Mode definition register to 1. When target

mode is activated the External Field Detector is automatically enabled by setting bit en_fd in the Auxiliary

definition register.

When bit targ is set and all bits of the Operation control register are set to 0, the ST25R3911B is in low power

Initial NFC Target Mode.

In this mode the External Field Detector with Peer Detection Threshold is enabled.

There are two different NFC target modes implemented (defined by mode bits of the Mode definition register): the

bit rate detection mode and normal mode. In the bit rate detection mode the framing logic performs automatic

detection of the initiator data rate and writes it in the NFCIP bit rate detection display register. In the normal mode

it is supposed that the data rate defined in the Bit rate definition register is used.

ST25R3911B

Application information

DS11793 - Rev 6

page 44/116

ST25R3911B Datasheet(PDF) 44 Page - STMicroelectronics

ST25R3911B Datasheet(HTML) 44 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL