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[v2-11] 2016-Jun-13

AS3911 − Application Information

NFC Field ON Commands

These commands are used to perform the RF collision

avoidance and switch the field on in case no collision was

detected. The Collision avoidance threshold defined in the

External Field Detector Threshold Register is used to observe

the RF_IN inputs and to determine whether there is some other

device, which is emitting the 13.56 MHz field, present close to

the AS3911 antenna. In case collision is not detected the reader

field is switched on automatically (bit tx_en in the Operation

Control Register is set) and an IRQ with I_cat flag in Timer and

NFC Interrupt Register is sent after minimum guard time

defined by the NFCIP-1 standard to inform the controller that

message transmission using a Transmit command can be

initiated.

In case a presence of external field is detected an IRQ with I_cac

flag is sent. In such case a transmission cannot be performed,

NFC Field ON command has to be repeated as long as collision

is not detected any more.

Command NFC Initial Field ON performs Initial Collision

Avoidance according to NFCIP-1 standard; number n is defined

by bits nfc_n1 and nfc_n0 in Auxiliary Definition Register.

Command NFC Response Field ON performs Response Collision

Avoidance according to NFCIP-1 standard; number n is defined

by bits nfc_n1 and nfc_n0 in Auxiliary Definition Register.

Command NFC Response Field ON with n=0, performs

Response Collision Avoidance where n is 0.

Implemented active delay time is on lower NFCIP-1

specification limit, since the actual active delay time will also

include detection of the field deactivation, controller

processing delay and sending the NFC Field ON command.

Figure 38:

Direct Command NFC Initial Field ON

Start

RF On

TRFW

TIRFG

n x TRFW

TIDT

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