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AS3910

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

mode only the Target Activation Detector is running.

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 – refer to page 15, 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 AS3910 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 AS3910 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).

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.

8.13 ISO-14443A SELECT SEQUENCE

In the 14443A select sequence the commands REQA (also WUPA), ANTICOLLISION and SELECT are used. For the commands REQA and

WUPA the short frame is used, for ANTICOLLISION the bit oriented anticollision frame is used, for SELECT the standard frame is used.

Transponder replies to commands REQA, WUPA and ANTICOLLISION do not contain the CRC so the configuration bit crc_rx of the

Configuration Register 3 (address 03) has to be set to 1 (receive without CRC) before these commands are sent.

8.13.1 REQA and WUPA

Sending of these two commands is simple since they are implemented as the AS3910 direct commands (Transmit REQA and Transmit WUPA).

Procedure is the following (note that since the ATQA response does not contain a CRC the configuration bit crc_rx of the Configuration Register

3 (address #03) has to be set to 1 before this procedure is started):

1. Send the direct command Transmit REQA (or Transmit WUPA)

2. When all the data is transmitted an interrupt is sent to inform the microcontroller that transmission is finished (INTR due to end of trans-

mission)

3. When reception of the ATQA is finished and all data is in the FIFO an interrupt is sent to the microcontroller (INTR due to end of

receive), additionally the FIFO Status Register displays number of bytes (2 bytes in case of ATQA) in the FIFO so the microcontroller

can proceeded with downloading data from the FIFO.

Sending the direct command Clear before sending Transmit REQA and Transmit WUPA is not necessary.