AS3909 datasheet(56/77 Pages) AMSCO

56 / 77 page

AS3909/AS3910 – 56

ams Datasheet, Confidential: 2013-Oct [3-02]

A p pl i c at io n I n f o r m at i o n

At the moment presence of external the RF field is detected an

interrupt is sent (INTR due to nfc event). The microcontroller

can now activate the oscillator, regulators and receiver.

As explained in “Target Activation Detector” on page 19, the

Target Activation Detector may also be used to detect the

moment when initiator turns off its RF field. In case the delay

time, after which the initiator turns off its field after sending its

request, is known, this feature is not needed and the Target

Activation Detector can be turned off by setting bit nfc_t low

after presence of the initiator field is detected.

Next the direct command Unmask Receive Data has to be send

to put the Receiver and control logic in the receive mode. The

AS3909/10 is now ready to receive request from the initiator.

Procedure during the reception is the same as in case of the

ISO-14443 mode.

The target response is done in the same way as in case of the

ISO-14443 transmission, only that the command which actually

starts the transmission is either NFC transmit with Response RF

Collision Avoidance or NFC transmit with Response RF Collision

Avoidance with n=0. These two commands perform the RF

Collision avoidance procedure before actually starting the

transmission. In case an external RF field is detected during the

RF Collision avoidance procedure an interrupt is sent (INTR due

to nfc event) and the transmission is not performed.

Next the AS3909/10 expects a new request from the initiator.

In case the Target Activation Detector is still enabled an

interrupt will be generated when the initiator switch on its field.

This is additional information for the external controller, but it

is not required by the receiver. The receiver is already running,

reception will be done automatically and an interrupt will be

sent when reception will be completed (or when the FIFO water

level will be reached in case of a long request).

NFCIP Initiator

In case the AS3909/10 is an NFCIP initiator, the microcontroller

activates the oscillator and receiver and prepares everything

for transmitting as in case of the ISO-14443 transmission. The

transmission is actually executed by direct command NFC

Transmit with Initial RF Collision Avoidance.

Following events are the same as described in previous chapter

only that roles of the initiator and target are interchanged.

The Target Activation Detector may also be used in case of the

NFCIP initiator operation to detect the moment when the target

RF field turns on and off.

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