AS3911 datasheet(132/149 Pages) AMSCO

132 / 149 page

AS3911 – 132

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

is detected during RF collision avoidance the field is

switched on and an IRQ with I_cat flag set is sent to

controller after TARFG.

The reply which was prepared as in case of reader to tag

communication is transmitted using Transmit

command

After the message is sent the field is switched off. The

time between the end of the message and switching off

the field is defined in General Purpose Timer. In case a

new command from initiator is expected the General

Purpose Timer IRQ may be masked since controller does

not need this information.

In case a new command from Initiator is expected the

sequence loops through point 1. In case the target reply

was the last in a sequence (DLS_RES in case of NFCIP-1

protocol) a new command from initiator is not expected.

At the moment the field is switched off, a General

Purpose Timer IRQ is received and the AS3911 is put

back in the low power NFC Target Mode by deactivating

the Operation Control Register. NFC mode is changed

back to rate detection mode by writing the Mode

Definition Register.

AM Modulation Depth: Definition and

Calibration

The AS3911 Transmitter supports OOK and AM modulation. The

choice between OOK and AM modulation is done by writing

Auxiliary Definition Register bit tr_am. AM modulation is preset

by direct command Analog Preset in case the following

protocols are configured:

• ISO14443B

•FeliCa

• NFCIP-1 212 and 424 kb/s

The AM modulation depth can be automatically adjusted by

setting the AM Modulation Depth Control Register and sending

the direct command Calibrate Modulation Depth. There is also

an alternative possibility where the command Calibrate

Modulation Depth is not used and the modulated level is

defined by writing the Antenna driver RFO AM Modulated Level

Definition Register.

AM Modulation Depth Definition Using the ‘Calibrate

Modulation Depth’ Direct Command

Before sending the direct command Calibrate Modulation

Depth the AM Modulation Depth Control Register has to be

configured in the following way:

•The bit 7 (am_s) has to be set to 0 to choose definition by

the command Calibrate Modulation Depth

• Bits 6 to 1 (mod5 to mod0) define target AM modulation

depth

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