AS3911 datasheet(139/149 Pages) AMSCO

139 / 149 page

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

AS3911 – 139

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

is in Transparent mode, the External Field Detector output is

multiplexed to pin IRQ. This enables detection of external

target/initiator field and performing RF collision avoidance.

In case timing of the NFC Field ON command is correct for the

NFC active protocol which is being implemented, these

commands can be used in combination with the Transparent

mode. These commands are used to perform the RF collision

avoidance, switching on the field and timing out the minimum

time from switching on the field to start of transmitting the

message. After getting the interrupt, the controller generates

the message in the Transparent mode.

When bit en_fd is set and all bits of the Operation Control

Mode (same as in case of setting of targ bit, (see “NFCIP-1 Active

Communication Target” on page 130). In this mode initiator

field is detected. After getting an IRQ with I_eon flag set, the

controller turns on the oscillator, regulator and receiver and

performs reception in the Transparent mode.

Stream Mode

Stream mode can be used to implement protocols, where the

low level framing needed for ISO14443 receive coding can be

used and decoded information can be put in FIFO. The main

advantage of this mode over the Transparent mode is that

timing is generated in the AS3911 therefore the external

controller does not have to operate in real time. The stream

mode is selected in the Mode Definition Register, the operating

options are defined in the Stream Mode Definition Register.

Two different modes are supported for tag to reader

communication (Sub-carrier and BPSK Stream Modes). General

rule for Stream mode is that the first bit sent/received is put on

the LSB position of the FIFO byte.

After selecting the stream mode the Receiver and Transmitter

have to be configured properly (there is no automatic

configuration for the stream mode).

Sub-carrier Stream Mode:

This mode supports protocols where during the tag to reader

communication the time periods with sub-carrier signal are

interchanged with time periods without modulation (like in the

ISO14443A 106 kbit/s mode). In this mode the sub-carrier

frequency and number of sub-carrier frequency periods in one

reporting period is defined. Sub-carrier frequency in the range

from fc/64 (212 kHz) to fc/8 (1695 kHz) are supported.

Supported number of sub-carrier frequency periods in one

reporting period range from two to eight.

Start of receive interrupt is sent and the first data bit is put in

FIFO after the first reporting time period with sub-carrier is

detected. One bit of FIFO data gives information about status

of input signal during one reporting period. Logic 1 means that

the sub-carrier was detected during reporting period, while 0

AS3911 Datasheet(PDF) 139 Page - ams AG

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