AS3911 datasheet(138/149 Pages) AMSCO

138 / 149 page

AS3911 – 138

ams Datasheet, Confidential: 2013-Oct [2-03]

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

The Transparent Mode is entered on rising edge of signal /SS

after sending the command Transparent Mode and is

maintained as long as the signal /SS is kept high. Before sending

the direct command Transparent Mode the Transmitter and

Receiver have to be turned on, the AFE has to be configured

properly.

While the AS3911 is in the Transparent Mode the AFE is

controlled directly through SPI interface:

• Transmitter modulation is controlled by pin MOSI (high is

modulator on)

• Signal rx_on is controlled by pin SCLK (high enables RSSI

and AGC)

• Output of Receiver AM demodulation chain (digitized

sub-carrier signal) is sent to pin MISO

• Output of Receiver PM demodulation chain (digitized

sub-carrier signal) is sent to pin IRQ

By controlling the rx_on advanced Receiver features like the

RSSI and AGC can be used. The receiver channel selection bits

are valid also in Transparent mode, therefore it is possible to

use only one of the two channel outputs. In case single channel

is selected it is always multiplexed to MISO, while IRQ is kept

low.

Configuration bits related to the ISO mode, framing and FIFO

are of course meaningless in Transparent Mode, all other

configuration bits are respected.

Use of Transparent Mode to implement active peer to peer

(NFC) communication:

The framing implemented in the AS3911 supports all active

modes according to the NFCIP-1 specification (ISO/IEC

18092:2004). In case any amendments to this specification or

some custom active NFC communication need to be

implemented Transparent mode can be used.

There is no special NFC active communication transparent

mode, controlling of the Tx modulation and the Rx is done as

described above. The difference comparing to the reader

transparent mode is that the emission of the carrier field has to

be enabled only during Tx. This is done by writing the Operation

Control Register before and after Tx. Since with every SPI

command the Transparent mode is lost it has to be re-entered.

In order to receive the reply in active NFC communication mode

only the AM demodulation channel is used. Due to this the

Receiver AM channel has to be enabled, while PM can be

disabled.

Implementing active communication requires detection of

external field. Setting the bit en_fd in the Auxiliary Definition

Detection Threshold. When bit en_fd is selected and the AS3911

AS3911 Datasheet(PDF) 138 Page - ams AG

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