AS3911 datasheet(51/149 Pages) AMSCO

51 / 149 page

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

AS3911 – 51

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

Clear

This direct command stops all current activities (transmission

or reception), clears FIFO, clears FIFO Status Registers and stops

all timers except Wake-up timer (in case bit nrt_emv in the

General Purpose and No-response Timer Control Register is set

to one, the No-response timer is not stopped). It also clears

collision and interrupt registers. This command has to be sent

first in a sequence preparing a transmission before writing data

to be transmitted in FIFO (except in case of direct commands

Transmit REQA and Transmit WUPA).

This command is accepted in case en (bit 7 of the Operation

Control Register) is set and Xtal oscillator frequency is stable.

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

Transmit Commands

All Transmit commands (Transmit With CRC, Transmit Without

CRC, Transmit REQA and Transmit WUPA) are only accepted in

case the Transmitter is enabled (bit tx_en is set).

Before sending commands Transmit With CRC and Transmit

Without CRC direct command Clear has to be sent, followed by

definition of number of transmitted bytes and writing data to

be transmitted in FIFO.

Direct commands Transmit REQA and Transmit WUPA are used

to transmit ISO14443A commands REQA and WUPA

respectively. Sending command Clear before these two

commands is not necessary.

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

NFC Field ON Commands

These commands are used to perform the RF collision

avoidance and switch the field on in case no collision was

detected. The Collision avoidance threshold defined in the

External Field Detector Threshold Register is used to observe

the RF_IN inputs and to determine whether there is some other

device, which is emitting the 13.56 MHz field, present close to

the AS3911 antenna. In case collision is not detected the reader

field is switched on automatically (bit tx_en in the Operation

Control Register is set) and an IRQ with I_cat flag in Timer and

NFC Interrupt Register is sent after minimum guard time

defined by the NFCIP-1 standard to inform the controller that

message transmission using a Transmit command can be

initiated.

In case a presence of external field is detected an IRQ with I_cac

flag is sent. In such case a transmission cannot be performed,

NFC Field ON command has to be repeated as long as collision

is not detected any more.

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