AS3911 datasheet(31/159 Pages) AMSCO

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ams Datasheet

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[v2-11] 2016-Jun-13

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AS3911 − Application Information

No-Response Timer

As its name indicates this timer is intended to observe whether

a tag response was detected in a configured time started by

end of transmission. The I_nre flag in the Timer and NFC

Interrupt Register is signaling interrupt events resulting from

this timer timeout.

The No-response Timer is configured by writing two

No-response Timer setting registers: No-Response Timer

of the No-response timer are defined by setting bits nrt_emv

and nrt_step in the General Purpose and No-Response Timer

Control Register.

Bit nrt_step configures the time step of the No-response Timer.

Two steps are available, 64/fc (4.72μs), which covers range up

to 309ms and 4096/fc, which covers range up to 19.8s.

Bit nrt_emv controls the timer operation mode:

• When this bit is set to 0 (default mode) the IRQ is produced

in case the No-response timer expires before a start of a

tag reply is detected and rx_on is forced to low to stop

receiver process. In the opposite case, when start of a tag

reply is detected before timeout, the timer is stopped, and

no IRQ is produced.

• When this bit is set to 1 the timer unconditionally

produces an IRQ when it expires, it is also not stopped by

direct command Clear. This means that IRQ is independent

of the fact whether or not a tag reply was detected. In case

at the moment of timeout a tag reply is being processed

no other action is taken, in the opposite case, when no tag

response is being processed additionally the signal rx_on

is forced to low to stop receive process.

The No-response Timer can also be started using direct

command Start No-response Timer. The intention of this

command is to extend the No-response timer timeout beyond

the range defined in the No-response Timer control registers.

In case this command is sent while the timer is running, it is

reset and restarted. In NFCIP-1 active communication mode the

No-response Timer cannot be started using the direct

command.

In case this timer expires before the peer NFC device (a device

with which communication is going on) switches on its field an

interrupt is sent.

In all modes, where timer is set to nonzero value, it is a must

that M_txe is not set and interrupt I_txe is read via SPI for

synchronization between transmitter and timer.

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