AS3911 datasheet(139/159 Pages) AMSCO

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ams Datasheet

Page 139

[v2-11] 2016-Jun-13

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AS3911 − Application Information

Once the start of initiator message is detected, an IRQ

due to start of receive is sent, the framing logic switches

on a module which automatically recognizes the bit rate

of signal sent by the initiator. Once the bit rate is

recognized an IRQ with I_nfct flag set is sent and the bit

rate is automatically loaded in the NFCIP Bit Rate

Detection Display Register. Detection of bit rate is also

a condition that automatic Response RF Collision

Avoidance sequence is enabled). The received message

is decoded and put into the FIFO, IRQ is sent as after any

received message.

The controller sends direct command Go to Normal NFC

Mode, to copy the content of the NFCIP Bit Rate

Detection Display Register to the Bit Rate Definition

normal (the command Go To Normal Mode and reading

of received data can be chained). Since the Tx

modulation type depends on bit rate, the Tx modulation

type also has to be correctly set at this point. The

simplest way to do it is to issue direct command Analog

Preset.

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. Bits nfc_n1 and

nfc_n0 of the Auxiliary Definition Register are used to

define number n of Response RF Collision Avoidance

sequence. 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.

The reply, which was 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 in the General Purpose Timer. (The

General Purpose Timer IRQ may be masked since

controller does not need this information).

From this point on the communication with initiator loops

through the following sequence (during this sequence bits

nfc_n1 and nfc_n0 of the Auxiliary Definition Register have to

be 0 to produce Response RF Collision Avoidance with n=0):

After switching off its field the AS3911 starts the

No-response Timer and observes the External Field

Detector output to detect the switching on of the

initiator field. In case the initiator field is not detected

before No-response Timer timeout, an IRQ due

No-response Timer expire is sent.

AS3911 Datasheet(PDF) 139 Page - ams AG

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