AS3909 datasheet(31/77 Pages) AMSCO

31 / 77 page

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

AS3909/AS3910 – 31

Appl icatio n I n f o rm a t i o n

An interrupt due to end of transmission is sent when RF field is

switched off.

All NFC Transmit commands are only authorized in case the ISO

mode configuration bit nfc is set and the oscillator and

regulators are running.

Mask Receive Data and Unmask Receive Data

After the direct command Mask Receive Data the signal rx_on

which enables the RSSI and AGC operation of the Receiver (see

“Receiver” on page 11) is forced to low, processing of the

receiver output by the framing block is disabled, all received

modulation is rejected. This command is useful to block receiver

and receive framing from processing the data when there is

actually no input and only a noise would be processed (for

example in case where a transponder processing time after

receiving a command from the reader is long).

The direct command Unmask Receive Data is enabling normal

processing of the received data (signal rx_on is set high to

enable the RSSI and AGC operation, the framing block is

enabled. A common use of this command is to enable again the

receiver operation after it was disabled by the command Mask

Receive Data.

Another possible use is in case one wants that the receive

processing starts immediately after the transmit command

(usually the receiver operation is enabled 40 μs after the

transmission is terminated). This is accomplished by sending

the Unmask Receive Data immediately after the end of

transmission interrupt is received.

The command Unmask Receive Data has to be used in the NFC

target mode. The sequence implemented in the AS3909/10

supposes that every action is started with a transmit command,

after sending the transmit data, the receive mode is

automatically entered to process the response. Such a

sequence is always in place in case of the ISO-14443 reader

mode and also in case of the NFCIP mode where the AS3909/10

is the initiator. In case of the NFC target mode this sequence is

started by receiving the interrogator request. After the

interrupt caused by the first initiator request command Unmask

Receive Data is sent to force the AS3909/10 in receive mode.

The commands Mask Receive Data and Unmask Receive Data are

only accepted when the Receiver is operating.

AD Convert

A/D conversion of signal on AD_IN pin is performed; result is

stored in A/D Converter Output Register (see “A/D Converter” on

page 11).

Duration time: 42μs max.

This command is accepted in any mode where the oscillator and

regulators are running.

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